this is what the OP is saying there is only so much you can add to a game before it becomes a whole differant game you can't take an FPS and add a kick and a punch that wouldn't be enough now we need combos these combos become more complicated now we have True Crime but wait guns are now too overpowered they take away from my ability to kick you in the face make you back flip and break your neck mid flight to make guns only usable with a certain combo, now you have Mortal Combat. (more or less this is kind of what the OP is saying)
GW2 has a differant combat system then WoW, WoW is differant then Terra but really can you add them all together with out ripping off them? GW2's combat system is enough to keep me entertained. active enough to be challenging yet simple enough to enjoy.