(FWIW, I was only claiming 1.) I'm fairly sympathetic to 2(a), although I would have thought we could get better at it with the right training. I can see how 2(b) could be a problem, but I guess I'm not really sure (i) that akrasia is always an issue, and (ii) why (assuming we could overcome 2(a)) we couldn't decide mathematically, and then figure out how to "own" the decision afterwards.

To own it, you'd need to not mathematically decide; the math could only ever be a factor in your decision. There's an enormous gap between, "the math says do this, so I guess I'll do that", and "after considering the math, I have decided to do this." The felt-experience of those two things is very different, and it's not merely an issue of using different words.

Regarding getting better at making decisions off of mathematics, I think perhaps you miss my point. For humans, the process by which decision-making is done, has consequences for how it's implemented, and for the person's experience and satisfaction regarding the decision itself. See more below...

(This seems to have worked for me, at least; and stopping to do the math has at sometimes stopped me "owning" the wrong decision, which can be worse than half-heartedly following through on the right one.)

I'd like to see an actual, non-contrived example of that. Mostly, my experience is that people are generally better off with a 50% plan executed 100% than a 100% plan executed 50%. It's a bit of a cliche -- one that I also used to be skeptical/cynical about -- but it's a cliche because it's true. (Note also that in the absence of catastrophic failure, the primary downside of a bad plan is that you learn something, and you still usually make some progress towards your goals.)

It's one of those places where in theory there's no difference between theory and practice, but in practice there is. We just think differently when we're considering something from when we're committed to it -- our brains just highlight different perceptions and memories for our attention, so much so that it seems like all sorts of fortunate coincidences are coming your way.

Our conscious thought process in System 2 is unchanged, but something on the System 1 level operates differently with respect to a decision that's passed through the full process.

I used to be skeptical about this, before I grasped the system 1/system 2 distinction (which I used to call the "you" (S2) vs. "yourself" (S1) distinction). I assumed that I could make a better plan before deciding to do something or taking any action, and refused to believe otherwise. Now I try to plan just enough to get S1 buy-in, and start taking action so I can get feedback sooner.