I wrote neither off. I also didn't make an assessment based on only bad plays/weaknesses of one player, as you did.
Kanter has better hands and footwork. Favors has length and athleticism. It's hard to compare the two because both are still learning how to use their very different strengths/abilities. I think they work well together:
On offense, Favors runs the floor and finishes more fluidly in transition. He'll likely be better diving to the basket on PnR's as well. Kanter, given his hands and what looks like a good stroke, will be able to create more offense for himself from more spots on the court in halfcourt sets.
On defense, Kanter's solid base will keep plodding, low post players away from the basket. There will be no rebounds for anyone else. Favors is better defending the PnR and helping from the weakside.
It's hard to choose between the two. Favors has a long way to go in refining his offensive game. Kanter should be fine if/when the game slows down for him (and yes, this also isn't a sure thing). It's hard to project either at this point, but I'm glad the Jazz have both. They're already productive NBA players (albeit offensively challenged ones).