I'd say you've got two out of three there. Based on lines Chrysalis says (When she beats Celestia, she says "Ah! Shining Armor's love for you is even stronger than I thought! Consuming it has made me even more powerful than Celestia!"), her power doesn't depend on the magical strength of the pony she's feeding off, it's all about love, and alicorns don't necessarily love any more intensely than other ponies. The changelings would have been more powerful taking on alicorn forms, but it's clear that that isn't enough to win in one-on-one combat: The Mane 6 took out dozens on their own, and they weren't even warriors. Twilight was the only pony who actually had the ability to do a lot of damage in a fight, and arguably Pinkie. Shining loved Cadence much more than most ponies love other ponies, which gave Chrysalis the power to beat Celestia. When the two fought, Celestia was actually the one to attack first, and it was a fairly straight contest of strength which Celestia lost. You're right about the uncounterable nature of the love spell that defeated the changeling invasion though.
As for Discord and Sombra, you have good points. Especially with Discord. It seems fairly obvious that Discord is stronger than Celestia, as Celestia is powerless to stop him in Season 2, but at the same time, when Celestia cast a spell on the Elements, Discord didn't even TRY to do anything to overcome the protections of the one thing in Equestria that could stop him. As you said, that's a pretty clear indication that he knew it would be a waste of his time to try.
I'm assuming Sombra had some sort of power source: My best guess is that he fed off the negative emotions of his subjects, which caused a feedback loop where he became more evil and more powerful and caused more misery which looped until he was strong enough to fight the alicorns and win without the Elements of Harmony backing them up. Said power source would in fact be FAR more dangerous in the hands of an alicorn, even the version of an alicorn I intend to use in my story, where alicorn-ness is basically a force multiplier for magic, rather than an instant pass to godhood.
As for the precognition: If Celestia could see the future, the fic would turn out extremely differently. In fact, the entire fic would probably only last one or two chapters. As soon as Twilight finds out Celestia can see the future, her likely response would be to use that. She could make up her mind to do X, where X is a series of factors that could influence how the alicornified society would develop. If none of them work out positively, game over. As you said, you can't really argue with someone who sees the future with tremendous reliability. If one of them does turn out favourable, Celestia has no leg to stand on, and logically would have to give in. In fact, if it turns out that, for the fic to make logical sense, Celestia must have sufficient precognition to make this a possibility, I simply won't write it.
There are other potential reasons behind the first episode turning out as it did. Chief among them is that Twilight and the others THOUGHT they had to save Equestria, but in reality, Celestia was waiting to intervene. She wanted Twilight and the others to succeed, because the Elements would be stronger and have a better chance of working if they did, but if they were clearly outmatched, Celestia would have stepped in herself. (Even this is a risk, but I don't find it too difficult to believe Celestia would take some level of risk to get her sister back to her pre-NMM state.)
So, to summarise my stance:
Binary magic: Agree. Celestia is comparable to FAI: DIsagree.
As for the precognition: If Celestia could see the future, the fic would turn out extremely differently.
She could have a variant of the Pinkie sense - uncontrolled limited precognition. Or it could be that there are feedbacks such that in order for it to work she needs to avoid all involvement in the proceedings (which is why she works through agents so much) - and introducing an endemic threat would require her to basically recuse herself from her own civilization, which seems a bit much.
EDIT: I am now taking arguments for alicornism. Alicornism being the placeholder term I've given to the stance that all ponies should be alicorns. Please PM me or post here if you have a good one, or an argument against one of anti-alicornism's strongest points: Overpopulation/over-use of resources, magical abuse/existential risk, or upheaval of the respect ponies have for their rulers due to their alicorn status. I would prefer general arguments for alicornism over counter-arguments if possible. Deathist / anti-alicornist arguments are still fine to post here.
Disclaimer: I'm not sure if this is worthy of a discussion post, but I figured, given the amount of people on LW who like My Little Pony, it would have at least as many potentially interested people as a regional meet-up thread would, so I figured I'd give it a shot. If this is too trivial or frivolous for LW, feel free to tell me and/or downvote, and I'll refrain from such threads in future. A place where I could go to find some help instead of the Discussion section would also be greatly appreciated in such a case.
So I had an idea for a one-shot or small novella, depending on how the plot developed, about an argument between Twilight and Celestia. Twilight finds out she's immortal now that she's an alicorn, and Twilight then decides that, given the standard anti-death concepts that immortality is good, death is bad, and so on, they should turn everyone who wants to be an alicorn into one.
The problem is, I'm having a very difficult time coming up with actual arguments for Celestia.
- Celestia herself is immortal, she's lived for well over a thousand years, and she isn't horrifically depressed, so clearly, immortal life is worth living and there's enough stuff to do with an extended lifespan.
- For the purposes of this fic, it's possible to turn anypony into an alicorn. I'm likely going to go with the idea that the spell can only be used a few times a year, but that's still enough to turn anyone who wants it into an alicorn within a couple of decades via exponentiation: The first targets can all be gifted unicorns who can be easily trained to use the magic.
- In most of the "Immortality sucks" fics I've read, the only real argument that immortality sucks is that you have to watch everyone else grow up and die. If a large majority of the population were turned alicorn, this wouldn't be a problem anymore.
- Nothing in canon suggests that there's any sort of religion in Equestria. Even in fanfics I've read, I've only read one fanfic where someone made up an afterlife that some ponies believed in, and in many more that I've read, Celestia's name is actually used in place of God in various sentences, like "Oh for Celestia's sake!" Thus, it's unlikely they'd believe in an afterlife: Both in canon and the majority of fanon, the closest thing to a God appears to be Celestia herself.
I've come up with arguments for Celestia by roleplaying the argument out by myself, but I haven't come up with anything that Twilight can't just shoot down, and I'd prefer if the argument wasn't just Celestia getting steamrolled, and I'd like to do this by strengthening Celestia's side, not weakening Twilight's.
Is the argument for deathism really that weak? I've read over the Harry vs. Dumbledore deathism argument in HPMOR several times looking for ideas, and IIRC Eliezer actually claimed he steel-manned Dumbledore's position, but I don't find anything Dumbledore says convincing in the slightest, and ended that chapter feeling that Harry was the clear winner in that debate, and that's with Dumbledore having access to arguments that Celestia doesn't, given that in the Potterverse, nobody actually knows what it's like to be immortal, and Dumbledore believes in an afterlife.
Some other arguments I've come up with for Celestia:
Argument: We can't just have a massive ruling class.
Response: There's no need for alicorns to be royalty. "Princess = Alicorn, Alicorn = Princess" is only something that law and tradition dictate: They can be changed. After all, Blueblood is a prince and not an alicorn, and it's certainly possible for an alicorn to NOT be royalty, if the princesses wanted.
Argument: Harder to keep the populace in line, if everyone has more power.
Response: Celestia's not exactly going around fighting criminals herself with her alicorn powers, so Celestia being much more powerful than others isn't necessary to keep the peace. If anything, an alicornified populace is MORE likely to be able to govern itself: Atm, a pegasus criminal can only be pursued effectively by about one-third of police officers, for example.
Argument: Overpopulation.
Response: One response to this is the idea that, starting a year or so from a royal edict, ponies who wish to be changed into alicorns aren't permitted to give birth more than once or twice. A broader response is that "overpopulation" isn't actually a reason to oppose alicornification, it's just a problem that has to be solved in order to do it. Saying "There'd be overpopulation" and then forgetting about the entire idea would be like Twilight saying that they didn't know how she was supposed to save the Crystal Empire from being banished again when she got given the task, and responding to this by saying "Oh well, guess that's it, we may as well pack up and go home." rather than trying to actually solve the problem. That said, this is the only truly legitimate argument I've come up with, an argument that requires real thought to fully defeat, rather than an argument that has an easy response leap to my mind.
Argument: Mortals wouldn't understand the consequence of their decision.
Response: Again, several arguments for this. Firstly, there's no reason to believe the alicorn transformation is irreversible, even if it's not currently known how to transform it back. Secondly, Celestia can already predict the consequences, and since she thinks HER life is worth living, clearly there's a solid chance that other ponies will have their lives worth living as well.
So, the questions to ask:
Are there good arguments for Celestia I haven't thought of?
Are the arguments I've already posited sufficient to not straw-man the lifeism position, and to allow for a reasonable argument?
EDIT: I am now taking arguments for alicornism. Alicornism being the placeholder term I've given to the stance that all ponies should be alicorns. Please PM me or post here if you have a good one, or an argument against one of anti-alicornism's strongest points: Overpopulation/over-use of resources, magical abuse/existential risk, or upheaval of the respect ponies have for their rulers due to their alicorn status. I would prefer general arguments for alicornism over counter-arguments if possible. Deathist / anti-alicornist arguments are still fine to post here.