I'd argue that the people who don't know how to properly play their class are the ones who probably did nothing but Fates to level to 50. So, unless you're suggesting we nerf the levelling system to ensure that can't happen I don't think there will ever be a proper solution to this problem. The people who suck at using their skills to the fullest are the ones who never needed to use them in the first place, and with existing dungeon content, that's rarely the issue.