The OP wasn’t specific and I think it’s two things - abilities and world.
Abilities
Talents are great: they enable to player to decide complexity (actives / passives).
New abilities can also show up here as an option - at the likely expense of something older. Having everything at once can be crazy to balance.
In the past they’ve split and merged abilities. I can totally see these as talents: do you want Earth Shock and Wind Shear together (like in classic), or separately (like in WLK)?
That said, I don’t know many other MMOs but the other I play has 10 buttons. A few more if you have a pet, switch weapons or stances. Shooters are popular and… never mind. MOBAs typically have 3+1 abilities plus inventory. Like for real, what’s the actual point of having Arcane Shot and Steady Shot on hunter. Yes, I can explain, but if I want to hard cast, I’ll play mage.
Oh yes, that reminds me… having to stand still in combat feels very odd to me in this day and age.
World
By now there is a mountain of reputations and currencies. These are mostly visuals, I’d just put them behind a currency, sometimes even merge currencies.
Being Ambassador, Diplomat and Insane may have been sensible during BC / Wrath where that was the only side game, but with soon 11 content sets, it’s a bit of a mountain. Best exposed by the mount and pet collection. Also, many mogs still require something arcane.
I’m also a big fan of just teleport points, and minimizing phasing. Teleport is somewhat redundant with mounts, except it gets tiresome to visit the same portal hubs every few minutes.
Mages
It’s kinda weird because my hunter can basically two shot everything, whereas my frost mage requires 8-10 abilities to take down a single creature. I’m happy with the latter but it’s a bit of an imbalance there.