these issues never surfaced in "I, Borg" or "Descent" of course
Well, duh. There'd be no reason to. There was no fighting of ANY kind in
I, Borg and there was no collective in
Descent so that was a whole other ball game altogether. He only snapped when he felt he was going to lose to them again, which never came close to happening in either episode.
That's not what's conveyed in the film. Lily calls him on his b.s. in the ready room scene and shows him that it's really about revenge, NOT losing to the Borg.(at this point, they think setting the auto-destruct sequence on the Ent-E will defeat the Borg, so he's not fearing losing to them.)
So if all he wanted was revenge, he could have had it in "I, Borg" since Geordi and Data give him a way to do that through Hugh. Yet he's not obsessing about revenge there.