1- Posiotionals.
A: they account for less than 1% of your dps so they don't feel rewarding to land.. ninja ignoring flank on armor crush loses a whole 2 potency per second on dps. monk ignoring demolish loses roughly 3 potency per second. sam and drg are about the same as well. and
B: because so many bosses don't even have them recently, they're pretty much obselete anyway.

2- Scripted encounters:
The cause of so many of the games issues is how scripted and predictable encounters are.. healing/ tanking is seen as boring cos the incoming damage is predictable. one reaid wide eveery minute... and thus they haven othing to do but spam 1 1 1 1 1 1

3- Vulnerability stacks:
At least in the current form. it doesnt punish the player who makes the mistakes it punishes the healers. they should make those debuff s criple the player so instead of now you take 10% more damage and the healers have to work harder. now its you dela 10% less damage. 20% 30% depending on how many stacks you eat..

4- The focus on dps and 2 minute damage buffs.
bring back utility, crowd control, actual resource management other than build some guage press a button..