a few of these could be swapped, so not a unique solution

As Paul mentioned, V could swap with C and M leaving valid groups; U (and potentially Y) could swap with at least O and I directly; and O could also do a chain swap replacing J/R/C, which replace U, which replaces O. It's a cool idea for a grid, but since it leaves the clues all so open-ended, I think it's especially important that the solution be pristine/unique.

(Also the C category is accurate, but without something to signal it, definitely harder than the others to come up with, as it's less about the letters themselves.)

Yeah nah, this doesn't work.

I think it's a bit more than Hamburger said. It's not only that this doesn't work; it's that no matter what your categories it will probably never work.