Why does it seem like people don't even read anything before they comment? The OP provides specific examples where a player, not due to a disability of any kind, is simply refusing to use the abilities he has at his disposal. I suppose if I was able to look through the aether at my fellow player and see he's missing fingers from his hands I will applaud him for the effort he's putting in, because it would still be significantly more than what I see from a lot of players. Simply not using Gauss Barrel because you don't like the cast times? Maybe you should play something else? I don't like cast times on Bard either, but I do it because that's the right way to play it. I don't determine what's the right way to play a job, Yoshi does that. The game does show you how you should be combining your abilities. Remember back to leveling Black Mage and the tutorials where the sole purpose was to teach you what Astral Fire or Umbral Ice are. You can't say the game doesn't tell you how to play. It does a fairly good job at showing you how without straight up playing the game for you. Time to find a better excuse for chronic-underperformers.

PS: This isn't limited to just DPS; this includes healers and tanks, too.