Which are the 'extraneous additions'?

Omniscience and omnipotence have already been discussed at length - the SA does not imply perfection in either category on the part of the creator, but this is a meaningless distinction. For all intents and purposes the creator would have the potential for absolute control over the simulation. It is of course much more of an open question whether the creator would ever intervene in any fashion.

(I discussed that in length elsewhere, but basically I think future posthumans would be less likely to intervene in our history while aliens would be more likely)

Also, my points about the connectedness between morality and utility functions of creator and creation still stand. The SA requires that the creator made the simulation for a purpose in its universe, and the utility function or morality of the creator evolved from something like our descendants.

But at any given time you may be in a branch that's going to be deleted or rewound because it doesn't lead to the results that the simulators want. The vast bulk of our experience would be in lines that the simulators don't want.

Not necessarily. It would depend on how narrow they wanted things and how often they intervened in this fashion. If such interventions are not very common then the majority of experience will be in universes which are very close to that desired by the simulators.

but the conclusions jacob cannell drew are still extraneous additions to the simulation argument, not necessary consequences of it.

No disagreement there.

No. You are assuming that the simulators are evolved entities. They could also be AIs for example

AI's don't just magically pop out of nothing. Like anything else under the sun, they systemically evolve from existing patterns. They will evolve from our existant technosphere/noosphere (the realm of competing technologies and ideas).

I would be surprised if future posthumans, or equivalent Singularity-tech aliens, would have moral systems just like ours.

On the other hand, moral or goal systems are not random, and are subject to evolutionary pressure just as much as anything else. So as we understand our goal systems or morality and develop more of a science of it, we can understand it in objective terms, how it is likely to evolve, and learn the shape of likely future goal systems of superintelligences in this universe.

Your insect example is not quite accurate. There are people right now who are simulating the evolution of early insects. Yes the number of researchers is small and they are currently just doing very rough weak simulation using their biological brains, but nonetheless. Also, our current time period does not appear to be a random sample in terms of historical importance. In fact, we happen to live in a moment which is probably of extremely high future historical importance. This is loosely predicted by the SA.

We do have a methodology of assigning probabilities to different types of simulators. First you start with a model of our universe and fill in the important gaps concerning the unobservables - both in the present in terms of potential alien civilizations, and in the future in terms of the shape of our future. Of this set of Singularity level civilizations, we can expect them to run simulations of our current slice of space-time in proportion to it's utility vs the expected utility of simulating other slices of space-time.

They could also run and are likely to run simulations of space-time pockets in other universes unlike ours, fictional universes, etc. However a general rule applies - the more dissimilar the simulated universe is to the parent universe, the vaster the space of configurations becomes and the less utility the simulation has. So we can expect that the parent universe is roughly similar to ours.

The question of evidence for intervention depends on the quality of the evidence itself and the prior. The SA helps us to understand the prior.

Before the SA there was no mechanism for a creator, and so the prior for intervention was zero regardless of the evidence. That is no longer the case. (Nor is it yet a case for intervention)