OK, I harp on this all the time, but I'm tired of people with no skills. Seriously, I might as well be partying with a level 30 as with so many people's level 90s now. Hard to believe people take pride in having useless jobs end-game; personally I wouldn't even put up my seek flag for anything other than a skill-up party.
I suggest you INCREASE the damage penalty, decrease the chances of a defensive skill proc, decrease the efficiency of cures and such, and increase the resist rates to magic proportional to the difference between a player's skill and the skill cap for their level, however, make the use of any still yield as much hate as if the skill was fully capped.
Maybe then the right players would die first in end-game and we could sort out the slow learners from the fast based on who can take a hint!
Honestly, offensive skill is easy to do now if you just take the time and effort; defensive skills are supposed to be fixed down the road, but they'll probably do it faster if more people are screaming about how their 90s are dying too much.