These are totally minor complaints compared to the above, but mine is pull uncertainty.

If the tank has been prebuffed with with a shield or similar, the healer is ready. Waiting until Divine Benison wears off, while probably not intentional, is aggravating and a waste of my skills.

For the love of Zodiark, once a tank starts running to the boss like they are going to pull, they really need to pull. Nothing like 3 or 7 other people popping cooldowns and precasting just to have the tank stop, so you cancel, then a second later they go. Please commit.

If a tank wants to pull wall to wall, fantastic, I'm right there and ready. But spending 3 globals on one trash pack, waiting for everyone's aoe to pop underneath, and then running to the next pack--it's a waste of time. All that wasted dps make the second half of the large pull worse because we spent our cooldowns running instead of smacking.