I'm still catching up on the other threads, but on one of them somebody was talking about David stealing powers from other Epics. I buy into this idea of David "collecting" powers from them, perhaps through touch. It would be thematically appropriate as he's collected information about their powers for years, and I read through a few key parts at the end of Firefight that might tie in with this. Oblivion touches David's shoulder before he teleports away, and then later when David seems to teleport away from the collapsing force field Prof creates around him, this is before Megan is fully reborn. As for Prof, he does gift David powers, but again he touches him and it might seem like Prof is gifting them, but David's actually also absorbing them, which might explain why he took so much healing power.
That is, of course, if David is actually an Epic!
Sorry if somebody has already made all these points, I'm new and haven't had a chance to read everything yet.