The important detail about hex is that it only affects ability checks, not attack rolls or saving throws. How often do enemies really make ability checks? -Perception to see hidden characters -Contested athletics/acrobatics to avoid being shoved.
Hexing all ability scores would have roughly the same effect as hexing only the targets dex or str (whichever is higher).
Hexing enemy NPCs makes them aggro you, which kind of defeats the purpose of lowering their perception to aid you in stealth. It (cursing Wisdom) is conceivably useful for pickpocketing where traders may/may not get a perception check. But given pickpocketing in the game is implemented as a gimmick/legal exploit (quick, no risks, huge rewards) with realistically guaranteed success when you know what to do/can easily savescum, it really doesn't matter
