Am I the only one who thinks (depowered) Q is actually trying to fix the timeline, if only to get his powers back?
I hope it's something like that!
IMO, Q (even a depowered Q) works much better as a plot device than an adversary.
It's not really all that fun having a nearly omniscient/omnipotent adversary because then the plot twists etc. required for the protagonists to prevail - just have so much less meaning.