You say that observation shows many worlds. I say that the photon interferes with itself. I find the latter far more plausible than invoking multiple universes for the photon to interact with.

That's fine until you start talking about a magical collapse process that happens conveniently at sufficiently large scale. IMO postulating additional non-local, non-unitary, ftl, etc. collapse process is strictly more complicated.

Most modern interpretations have "collapse" as only a change in the description level, not a physical process.

You're right that postulates such as the projection postulate complicate the theory. But it's not clear how to explain experimental results, like the stochastic nature of measurements or the Born rule, without it. I can make a theory as simple as you like if you don't require it to explain experimental results.

Don't forget that the Copenhagen people also haven't really answered the Born problem, they just lump it into the black box of "collapse".

The many-worlds interpretation has no collapse at all. :-)

In QM random outcomes occur. By what mechanism are the random values chosen? Many Worlds has a plausible mechanism for this. I'm unaware of any other interpretation claiming the same.