Stats are useful but they can also cloud almost any issue. Surely, every sane fan agrees that it is best to be productive in every facet of the game, including the passing game. What Saban wants to do on offense is to be able to pass and run the ball effectively. Bama can do that with Tua, it cannot do that with Jalen. I don't see how having him as QB can reduce Bama's chances for going 12-0.
Most agree that Tua is superior to Jalen in every facet of the passing game. I would add that though Jalen is a good runner, he is not much better than Tua. In fact, I think Tua has the edge in some aspects of the running or non-passing game: better decision maker in most situations including RPOs, far quicker, much better pocket presence. The only edge for Jalen is top-end speed as well as strength and Tua is strong himself. Tua even has the edge in intangibles because of his well founded confidence. IMO, I think the fear of Tua turning the ball over has been overrated at this point. It may turn out to be true, but it hasn't yet shown to be an issue and has not been nearly as bad as Jalen toward the end of '16, especially the '16 AU game.
As things stand now, I will be very surprised and almost shocked if Bama doesn't go 12-0 - and Tua only enhances that prospect. It's not just because of Tua, but IMO, he does greatly enhance Bama's chances over any other QB on the roster.