This is pretty much a solved problem in languages with multiple dispatch (Common Lisp, Julia, Raku etc), the behavior lives in the methods which don't belong to

This is pretty much a solved problem in languages with multiple dispatch (Common Lisp, Julia, Raku etc), the behavior lives in the methods which don't belong to a specific class. You can sort of, kind of get there with free functions and overloading as long as you're not doing anything fancy with the methods.