Ah, I see now that we said almost the same thing.

Basically simpler hypotheses are on average more probable than more complex ones, no matter how complexity is defined, as long as there is a minimum complexity and no maximum complexity

Which is the basic receipt of Solomonoff induction!

But some measures of simplicity are more useful than others, and this is determined by the world we live in

I would only say here that simplicity is determined by the agent evaluating it, and while most agent are determined by the world that they live in, some might not.