Equivalently we can say that neither QFT nor string theory gains anything from the empty hand-waviness of the copehagen interpretation, Everett's many-world's, etc.

Those also don't really play a role in the professional life of a physicist, nowadays you really do stare at computer screens a lot and try to find things in data, it's not like physicists sit around and discuss many-world theory as part of their day job.

These are just the popular things that make it out into public discourse

Depends on the physicist. Those working on foundations of quantum mechanics do. There just aren't many of them.

For example the whole group around beyondspacetime.net does that.

Isn't that true of any of the major "interpretations" of QM? Copenhagen etc.

The others are simpler.

No they're not. There far more complex.

I'm layman but am biased against it being true as it is not as fun and exotic as many worlds, regardless of merit.