Green Lantern as a concept wasn't broken before Rebirth so the idea that Johns "fixed" it somehow seems weird to me? Johns's MO (on basically everything he's touched for the last decade) isn't so much fixing something as it has been to boil characters down to a one-sentence kernel that he expands outwards into a convoluted mythos. He's also not a continuity geek in the way, say, Waid or even Morrison are, and I think gketter's description of Ellis fits Johns just as well.
Ellis as a "fixer" seems even odder to me. Iron Man was a misstep, T-Bolts was a radical departure, the less said about Astonishing X-Men the better, Secret Avengers was cool but no one followed up on that so that leaves... Moon Knight I guess?
I dunno maybe I'm just misunderstanding of what you guys mean but when I think of writers who "fixed" characters or concepts I think of Morrison on JLA and X-Men or even the recent stuff Remender tried to do with Scarlet Witch