The term hybrid gets thrown around a lot, and it's such an elastic term that it pretty much fails at properly describing things. For instance, red mage could be a white mage and black mage hybrid, but it's not really in between those two job. It takes a little bit of both and combines it will a lot of enfeebling, a little support, and a dash of melee (not as much as many red mages like to pretend, but enspells, phalanx and composure are all melee buffs). They have access to all their abilities all the time, which means that they can be completely reactive to whats happening right now.
Scholars are a different type of hybrid. They do exist between the two extremes of white mage and black mage, but they specialize into one at the expensive of the other. My vision of scholar is a job that can hang with black mages when focusing on it (specifically by burning stratagems), or they can hang with white mage when focusing on it (again, but burning stratagems), but if they try to do both then they end up burning all their stratagems to switch between addendum white and black. I should also say that I have no problem with the specialized classes being a bit better then a scholar who is specializing, but if a specialist isn't available a scholar should be able to step in and play the role adequately.
Black mages sometimes grumble about scholars doing similar damage on single target nukes, but they have superior tools and a much deeper spell list to separate themselves as specialists. Scholars do fine on the nuking side of things because if you run out of stratagems you can nuke without for less damage, but it ultimately has little impact on the party. The issue with scholar is that the light arts side isn't strong enough right now, and in end game events you can't have healing suddenly drop off. It doesn't matter if you go the rapture or penury route to try healing with cure IV, you're going to run out of stratagems and pull hate from cure spam.