Logic that Aquaveil, Blink, Stoneskin, Dread, and Reprisal are their respective elemental "spikes" aside, the problem with those is similar to that we faced with Shield Mastery: Without being the mob's focus, they're pretty much useless. Granted, I like defensive enfeebles if done right, but offensive maneuvers tend to get the most use. This isn't to say the concepts can't be melded in some way, though.

For example, when we had another enfeebling thread in the past, my idea for a Pain enfeeble involved the amount of damage a mob does in a given attack directly subtracts from its ATK for its next attack round. This would basically diminish the amount of damage a hit does every other attack round, and with luck, could factor into the damage of a TP move if used in a low phase. This doesn't quite address how some mobs are simply given stupid high weapon damage ratings, but that's also another type of enfeeble that could be looked into.

Anyway, with Helix spells being improved for SCH, I'd want to so DoT enfeebles are largely out of our domain at this point. This isn't to say Poison III or something better than Bio III could land its way in our arsenal, but subbing SCH aside, we'll probably never personally see anything as good in our arsenal. And given the exploitation of various DoT tactics in the past, I'm not entirely surprised. Otherwise, to generalize, if there's a stat in the game, a buff or debuff can be made to affect it. There are lots of stats, just going beyond what we see on our screens. Much as I dread how I'd arrange my macros with dozens of new spells, they're possibilities.