There are many one off quests. Republic Roulette on Ord mantel, Meltdown on Coruscant., The Thousand Steps on Tython are 3 just from the top of my head.
There are. But that is not the norm, it's the exception in the hundred of hours of mission play in the game.
I accept that in some peoples minds.. they consider them worthless and don't do them, which is fine. But it does not change the context of my comments about missions.