Goblin Queen (She/Her/Hers)
Excellent points, all. I think broadening those categories would be the way to go, as I wouldn’t want more than about 6 categories. But if doing that makes the categories so broad as to be nonsensical or arbitrary, maybe it would be better to base them on source rather than end effect… Hmm…So, ignoring the source (spell, item, creature, etc.) and looking only at the end-result effect. OK, got it...except Enchanted and Cursed Items then stands out like a sore thumb as that's still looking at the source. Maybe change this one to just "Curse"?
That said, I think you either need more categories or to expand those already present, to account for:
Fear or Panic
AoE damage (fireball, lightning, cold, etc.)
Other; including corner cases, save-or-dies, and anything else not covered by an existing category.
And there's still death saves - the ones you make when unconscious and dying - that work differently again. Changing the terminology so these rolls aren't called "saves" would help.
And here the tricky bit becomes looking carefully at the relative power/usefulness/frequency of each category, so as not to nerf or over-boost any one class. For example, a bonus vs IC&P is way more useful (and thus, powerful) than a bonus vs Teleport, not only because IC&P usually comes up far more often in play than does Teleport but because those things are often very effective when they do.
I wouldn't worry about two or more classes ending up with the same set; if it makes sense that they would, let it happen.