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.
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.