And until there's a derivation of the Born probabilities, many worlds isn't necessarily simpler than a model with physical collapse.

I find that difficult to believe. Born probabilities are comparable to a law that causes particles to become disentangled, if you ignore the violations of the Tao of physics. In order to get a complete theory, you also have to have a law that causes particles to become entangled, and a law that causes particles to interact without ever becoming entangled.

Am I missing something?

(for example, in the most recent sequence rerun)

Please link when you do that. It's not going to stay the most recent sequence rerun.