I'd also like to point out that, for the past two years, we've heard a lot about Contreras "learning how to be a great catcher" from a defensive standpoint -- handling the pitchers was the weakness that, supposedly, kept him at AAA for a few years -- and there has been *none* of that talk this spring. The only buzz about Willson has been how he is "ready to take off" after solidly becoming one of the top 10 catchers in MLB. (Remember Darvish's recent quote about being caught by his old buddy Gimenez -- "I'd rather have Contreras".)
Honestly, the only rap I've heard against Contreras is his pitch-framing skills, and seeing as he is one of the top four catchers in MLB in terms of throwing out runners (pop time, release time, throw speed, etc., all are elite), perhaps slightly weak pitch framing is considered less of a problem than if, say, he was just average in caught stealing and pick off stats.
So, Willson is now being treated as the veteran, from whom Caratini can learn a few things in his own development. Pitch framing aside.
And, to be honest, once the automated strike zone comes into play in five years or so, pitch framing (i.e., cheating by trying to make a pitch outside of the strike zone appear to have been a strike via sleight-of-hand) will become a completely non-useful skill. So, why put millions of dollars into players who have a skill that is akin to being the best at making buggy whips? Yeah, there is still a market for the skill at the moment, but, just like with the best spit-ball pitchers of 70 years ago, it's a skill that won't do you any good after a little more evolution of the game.