I wish to hell that I could just not bring up quantum physics. But there's no real way to explain how reality can be a perfect mathematical object and still look random due to indexical uncertainty, without bringing up quantum physics.

MWI doesn't explain why the Universe has four large dimensions and three small neutrinos. In order to explain that by indexical uncertainty, you have to bring up other multiverse concepts anyway, and if you bring in "ultimate ensemble" theories, then MWI vs. non-MWI no longer matters for the rhetorical point you're making.

I am personally unconvinced by the arguments that MWI does away with the need for a non-unitary operation, because of the inability of MWI proponents to show that MWI works in a rigorous way without one. I would bet that some combination of Objective Reduction + MWI is the correct physical theory. The point I'm trying to make is that the Eliezer's conclusion about indexical uncertainty may still be correct, even if you find Everett's MWI incoherent.