Well, at least we have Sphinx to "finish" Ouma off...
Himeji, from the way you're telling, I can't help but think you made it sound as if picking up a grimoire is as if standing next a bookshelf in a library and pulling out a book out from it. Ouma's arc clearly demonstrated what will happen if your ordinary magician were to try to access the Index Librorum Prohibitum, and Ouma can't cope with it.
And because of that, he learnt his lesson (and him learning Touma has that hand called Imagine Breaker which can dispel anything within contact kinda make his whole adventure to find Index
pretty useless) and have suffered enough consequences that Touma just made Sphinx deliver the "final blow" instead (as "punishment" for ruining his homework). Awaki? She just ran away without learning her lesson.
Accelerator on the other hand was trying to do Last Order a favor by stopping people from gathering the Remnants, and as the central guy in the Level 6 experiments, he pretty much knew the reason why Last Order wants Awaki to be stopped as she's one of the culprits behind the gathering of the Remnants.
Him punching Awaki to a brutal knockout rather than direct to the graveyard, is still pretty
kind of him. If he still had that Level 6 Experiment personality back then, we won't get to see her again beyond this point.