In both MWI and collapse, parts of the wavefunction effectively disappear from the observable universe (or as MWI folks like to say "the world I find myself in.") MWI adds the extra and completely gratuitous postulate that this portion of the wave function magically re-appears in another, imaginary, completely unobservable "world", on top of the gratuitous extra postulate that these new worlds are magically created, and all of us magically cloned, such that the copy of myself I experience finds me in one "world" but not another.

This does not correspond to the MWI as promulgated by Eliezer Yudkowsky, which is more like, "In MWI, parts of the wavefunction effectively disappear from the observable universe -- full stop." My understanding is that EY's view is that chunks of the wavefunction decohere from one another. The "worlds" of the MWI aren't something extra imposed on QM; they're just a useful metaphor for decoherence.

This leaves the Born probabilities totally unexplained. This is the major problem with EY's MWI, and has been fully acknowledged by him in posts made in years past. It's not unreasonable that you would be unaware of this, but until you've read EY's MWI posts, I think you'll be arguing past the other posters on LW.