The reason this works in pvp is because of how much theyve simplified the jobs.
For example DRK doesnt have Dark Arts in pvp.
This would greatly effect the way you use your combo, you'd have to pay real close attention to know which part of the combo you're on in order to know when to hit dark arts, you won't be able to rely on muscle memory, you'll have to watch your hotbars all the time.
Same goes for using Blood of the Dragon, or Duality, etc.
So in actual fact consolidating combos would make things more complicated, because outsude of pvp combos dont exist in a vacuum, they all have interactions with other skills.