So this is a random idea I had.

Maybe there should be defensive UV's, not talking about status resist or defense increase but UV's that give you a percentage damage reduction versus enemy types / in general / whatever.
Not entirely sure on the name but for the sake of argument let's call it Damage Protection / Vulnerability (of course, this does mean it could be confused with Damage Bonus since they both start with "damage" but whatever)

I imagine it would be:

Low: 8.3% reduction
Medium: 16.7% reduction
High: 25% reduction
Very High: 33.3% reduction
Ultra: 41.7% reduction
Maximum!: 50% reduction

or something similar (obviously max would be really hard to get)
With this you could do stuff like add Damage Protection vs. Slimes & Beasts Medium to each piece of the jelly sets, maybe give plate armour a low reduction to everything per piece and slap Damage Vulnerability vs. everything Low on BK/Chaos/whatever.

Obviously you could get these as random UV's on your armour, but probably only the specific variants similar to damage bonus. (Maybe it also only goes to Medium as a UV)

For example, if you're doing an FSC run and you use Dread Skelly armour: medium per piece goes to Very High, so you take 2/3 damage, and if on one of those pieces you got Damage Protection vs. Undead Medium then the slags deal 1/2 damage to you.