What you know when you know nothing
50⁄50 are the odds of A when we know nothing about A. If we know that we don’t know anything (but that we know that we don’t know), then we can infer that any statement C that is “A and B” is 25% true.
If you buy that the term “singularity” correctly implies that we won’t know anything about the world after AI reaches a certain treshold, then we know that most complex statements (statements formed of long conjunctions) won’t be true in that world.
We can only make that inference about conjunctions if we know that the statements are independent. Since (by assumption) we don’t know anything about said world, we don’t know that either, so the conclusion does not follow.
Then I guess the OP’s point could be amended to be “in worlds where we know nothing at all, long conjunctions of mutually-independent statements are unlikely to be true”. Not a particularly novel point, but a good reminder of why things like Occam’s razor work.
Still, P(A and B) ≤ P(A) regardless of the relationship between A and B, so a fuzzier version of OP’s point stands regardless of dependence relations between statements.