[ASoT] Probability Infects Concepts it Touches

Does an asteroid perform optimization? We can predict its path years in advance, so how "low-probability" was the collision?

It does, because in the counterfactual world where the asteroid didn't exist, the collision would not have happened.
The "low probability" refers to some prior distribution. Once the collision has happen, it has probability 1.

Suppose you view optimization as "pushing the world into low-probability states."

That is the source of your confusion. Because once an event has happened, it has probability 1. But the event will happen, so it already has probability 1.

The time-bound perspective on this is: a sufficiently powerful predictor can anticipate the effect of the optimization. But it still requires the optimizer to actually perform the optimization, through its actions/existence.

The timeless perspective on this is: the mere existence of the optimizer shifts (or rather, has already shifted) the probabilities in the world where it exists towards the states it optimizes for, compared to the counterfactual world where that optimizer does not exist.

Does the bible perform optimization (insofar as the world looks different in the counterfactual without it)? Or does the "credit" go to its authors? (Same with an imaginary being everyone believes in)

Credit does not have to add up to 100%. Each of the links in a chain is 100% responsible for chain maintaining its integrity. If it would fail, the entire chain would fail. If a chain has 10 links, that adds up to 1000%.

I suspect I’ve been nerdsniped by a wrong question somehow.

"What if X happened?" means "what if X happened, and the set of things I can and do think of when analyzing events in the implied context otherwise stayed the same?" This set doesn't include a complete causal chain (and, since you're a finite human, couldn't possibly do so.)

"What if quantum computers could solve P-=NP?" doesn't mean you should consider the effect that quantum computers have on other things because when you think about those other things your chain of reasoning normally won't go all the way back to the relevant math and physics.

You could choose to go back to math and physics anyway, but by doing so you are misreading the question--the question implies "only go back as far as you normally would go." You could also say "well, the implied context is 'make deductions about math and physics'", in which case yeah, it's a good objection, but you may not be very good at reading implied contexts.

I think an optimizer is a thing that makes decisions that are aimed at optimizing a certain quantity.  I think, when you talk about what a decisionmaker does and its effects, you're essentially saying "What if their decisions were this, vs what if their decisions were that?".  If you say "Well, actually their personality and known objectives dictate that their decisions would (almost certainly) be this", then you're not considering them as a decisionmaker, but as one of the fixed features of the world.

It is arguably the case that, along the lines of your analogies, the general question of "What if their decisions were different?" is sometimes divorced from reality—e.g. "Yes, the dictator's bodyguards do have the power to kill him, but they've also been selected for being loyal and unlikely to do that, so it doesn't make much sense to talk as though that's a real possibility."  Though, at least to my knowledge, humans are sufficiently unpredictable, and things like unexpected mental illness can happen, such that you can never really say the chance is zero that a human will decide to do something.  With a computer program, you can get a lot closer to certainty—but there are gamma ray bitflips and such.  So I would say, it's pretty much always physically possible for the decisionmaker to pick anything; whether it's likely is a different question.