As nice as Haste is, it's pretty much OP in every game it's in to the point where it becomes a necessity, and if it isn't a necessity then it makes fights trivial. If that happens then any future support jobs are going to need to have Haste just to be able to compete.
You only really need to look at it in F11 to see why they are very hesitant about it.
They released a headpiece for all jobs that had Haste on it and that became a required piece of gear for all jobs for several years. It was silly seeing everyone in-game with a turban.
