In quantum mechanics we have the the state of a system represented entirely by a wave function, and the equation that dictates how it will evolve, i.e. the Schrodinger equation.
The Copenhagen interpretation requires, in addition to the above, the claim that the wave function "collapses" due to something called a "measurement", and the Born rule, which tells us that the probability distribution of collapse is given by the square norm of the wave function, and the basis in which the measurement is occurring. This is a claim about an additional mechanic to the Schrodinger equation, in describing how the wave function evolves.
The spontaneous collapse theory requires additional mechanics to determine the time-dependent probability distribution of spontaneous collapses (which favors the spatial basis), in addition to the Born rule. Like the Copenhagen interpretation, this is another additional mechanic to the Schrodinger equation in describing the wave function's evolution.
The De-Broglie Bohm theory requires the existence of a point particle in addition to a wave function. And, as with spontaneous collapse, it elevates the position basis as the "most important" one.
It seems like the Everettian interpretation is the only one that adds nothing to the theory, and simply states that the wave function and the Schrodinger time evolution is all there is. It doesn't require the Born rule. It doesn't favor a specific basis of states for the wave function, like spontaneous collapse or pilot wave does. And it doesn't add any new mechanics to the evolution of the wave function beyond the Schrodinger equation. It seems like the set of assumptions in any other interpretation of quantum mechanics is a superset of the set of assumptions in the Everettian interpretation.
Am I missing something? Does the Everettian interpretation impose something new to quantum theory that the others don't? Or is the Everettian interpretation the interpretation with the fewest assumptions, and thus the correct application of Occam's Razor to the measurement problem?
Note: I am not asking if the Everettian interpretation is correct, or "obvious", or the one that everybody should be adopting and textbooks should be teaching. Nothing like that. I'm asking if the Everettian interpretation of quantum mechanics is the one with the fewest assumptions. I can already foresee the objections that this question is ultimately subjective and opinion-based, which it would be if I was asking the former questions. But I think the question I'm asking is actually objective. It's perfectly compatible to believe, for example, that Everettian is the natural choice when applying Occam's Razor, but still not believe that it's the correct interpretation.