My opinion: I think the argument that FATE leveling produces bad players while having to run (5-10 dungeons, 1 time each while leveling) makes a great player has no merit. Solo questing (minus the class quests, which even if you are FATE grinding you still have to do) doesn't magically make someone a good group player. Neither does doing a handful of dungeons while leveling. So, regardless of FATE grinding or not, people will be bad at level 50. Some will get better, others will not.