Aren't the highest level abilities ridiculous enough as it is? I don't think raising the cap is a wise choice, the game already is kinda lacking in 14+ challenges, remedied somewhat by the DLCs.
I wouldn't say so. Can't think of anything so ridiculous. Actually, I didn't even use my 20th level abilities as a Paladin, I didn't like them, decided to take some passives instead.
Of the wizard's spells, I tried meteor shower a couple of times. Yeah, it was powerful, but with its red-only circle of AoE, you have to be careful for friendly fire.
In Deadfire, with abilities power scaling with your power level, it's possible for an early-level ability to be continuously useful throughout the game.