The problem is that PvE endgame (idk about PvP, I gave up in Legion) requires you to min-max the !@#$ out of your character, which leaves little to no room for customization. I'd like to have, e.g. Mage talents to increase the distance you can Blink to, or to increase the damage absorbed by Frost/Prismatic/Blazing barrier, or to create decoys of yourself (like Jandice Barov in Scholo), at the cost of raw output. But you can't really have that these days, can you? Especially when every ounce of DPS matters.