First, I think there's no real QB battle. We've seen AJ vs. Phillip, Sims vs. Coker, Coker vs. Bateman, and Hurts vs. Barnett. This isn't that, and even then the outcomes were somewhat telegraphed. If Tua is healthy and behaving himself, he's the starter, I can't really imagine another outcome.
Having said that, Saban made Alabama a championship contender out of a JPW lead team. Feel free to look up JPW's stats and Alabama's offense during that period, you can check out the recruiting as well. They were far short of a juggernaut offensively, they were not loaded with 5 stars. Then, the following year they win a championship with a sometimes struggling QB who was hurt in the championship game and threw for 58 yards.
Sure, things have changed a bit, but Alabama's offense has consistently put up a similar number of yards and points no matter who the QB was. They went to a championship game with a true freshman Hurts, who was the worst throwing version of Hurts, and they still almost won a championship then to.
I've seen data to indicate Alabama is actually at their best when they lean on a strong running game instead of a strong QB, and I say this not to argue for Hurts starting, that should be Tua, but that the engine for success at Alabama is defense and running the ball. Would centering the offense around Hurts have been a setback in terms of losing some skill players? Yes, it would have. But I find the idea that Saban has a house of cards that would have just fallen down to be hard to buy. He won with weaker classes than he had last year, he's won with 3 star guys, and should I remind everyone Alabama won championships with the wishbone? The wishbone turned an NFL QB factory into a completely different offense. Alabama still won didn't they?
If Saban adjusted his offense to a less pro-style offense, one could argue he'd find more success in some areas. I'm not saying that should have happened, or I wished it would have happened, but I think people saying Saban couldn't handle a Hurts as the starter type scenario seem to miss the obvious. He went to two championship games under that scenario, without even having an offense that fit the personnel. If his hand was forced to go all the way down the road, he'd compensate for loss of personnel with an offense that better fit who he did have.