Hi! My main issue with this is not that P(“2+2=4”) = 0.99 is extravagant, but rather that it allows us to use the Bayesian framework to make judgments about the Bayesian framework itself. Such self-referential instruments/mixing metalanguage with the object language usually require additional care in mathematical logic and can be dangerous (e.g., the liar paradox).
Don’t you find the application of law of the total probability to the statement/event “law of the total probability is true”, with a prior of P(“law of the total probability is true”) = 0.99, at least slightly problematic? The one issue: law of the total probability (on the meta-level) requires us to consider both cases (with appropriate weights): law of the total probability is true and law of the total probability is false, but if we assume it is false, then the very application of the law of the total probability is unjustified. This is very similar to liar paradox.
P(“2+2=4”) = 0.99 induces similar complications.
I think you are slightly misrepresenting the pro-objective-collapse position. A collapser believes in collapse not because the many-worlds interpretation seems too bizarre to be true, but simply because, for him, it is an experimental fact -- the evidence B. To be more precise: it is a fact that he (his consciousness, soul, etc.) directly observes that the cat is dead, which means the state is somehow selected. For him, the real question is why this particular state is realized and why he experiences it.
Of course, one could argue that the state is not preferential since his quantum clone observes the cat as alive. But then, why is he not his quantum clone? One could respond with something like “by definition,” “because you are who you are,” or “this is just a semantic issue,” or "it all sums up to normality", but I think such explanations are perceived by him as mere curiosity stoppers because they are not helping concentrate the probability mass in any way.
By the way, I am not a collapser -- hence why I am using “he” instead of “I” -- just pointing out that your criticism addresses a different and much weaker argument than the one typically held by those who believe in collapse.