A core element that makes many skills more useless is still the armor system, because heavy damage skills are more preferable to low damage CC skills for a huge part of the fight. It's also the reason why water/air is inferior to fire/earth.

Also Flat-stat buffs totally lose they worth the more the game progresses, because +1 does not make a real difference if you already have stats that are 20+. (Also the reason why stuff like food is not that valuable.)