I'm probably misunderstanding or simplifying his position
You really aren't. His logic is literally "it's simpler, therefore it's right" and "we don't need collapse (or anything else), decoherence is enough". To be fair, plenty of experts in theoretical physics hold the same view, most notably Deutsch and Carroll.
Doesn't pilot-wave QM imply literally the exact same calculations happening as for MWI, though?
I sort of got that idea, but if that's true then I'm not sure I see what the difference between them is in the first place. It seems to me that any theory of quantum mechanics which practically differs from MWI must include collapse somewhere.
(Assuming the difference you're looking for is "People don't live in the other branches".)
What is something you used to believe, preferably something concrete with direct or implied predictions, that you now know was dead wrong. Was your belief rational given what you knew and could know back then, or was it irrational, and why?
Edit: I feel like some of these are getting a bit glib and political. Please try to explain what false assumptions or biases were underlying your beliefs - be introspective - this is LW after all.