If we’re imagining civilizations very similar to humanity, then the multiverse looks like ~100% of one of the options. Reality’s true answer will be very overdetermined; it is a failure of our map that we cannot determine the answer. I don’t know much about quantum physics / many-worlds, but I’d be pretty surprised if small fluctuations to our world made a huge difference; you’ll need a lot of fluctuations adding up to a lot of improbability before you affect a macro-level property like this, unless you just happen to already be on the knife-edge.
This doesn’t contradict anything you’re saying but there’s arguably a wager for thinking that we’re on the knife-edge – our actions are more impactful if we are.
[Edit to add point:] The degree to which any particular training approach generalizes is of course likely a fixed fact (like in the Lesswrong post you link to about fire). But different civilizations could try different training approaches, which produces heterogeneity for the multiverse.
This doesn’t contradict anything you’re saying but there’s arguably a wager for thinking that we’re on the knife-edge – our actions are more impactful if we are.
[Edit to add point:] The degree to which any particular training approach generalizes is of course likely a fixed fact (like in the Lesswrong post you link to about fire). But different civilizations could try different training approaches, which produces heterogeneity for the multiverse.