What we're seeing is demonstrated potential, which is at least a match for Varitek's.
A little secret for your consideration: Varitek, while he has decent tools, was never an elite defensive catcher until he learned how to use them. The Jason Varitek who spent those first couple years platooning with Hatteberg is not the Jason Varitek we saw in his prime. He had to learn some things to get there from here. He was 3-4 years older than Salty is now before you can really say with any certainty that he got it all down. Before then he had a reputation for actually being a bit of a butcher behind the plate, being a relatively poor receiver and defender generally (he frequently DH'd over a guy who never caught again after he left), and made up for it with half decent switch hitting offense.
Salty's arm is maybe not as accurate as Tek's was perhaps, but he's got all the talents Tek had and a reputation as a good hard worker. but it's going to take time -- years, probably -- for him to get it down and become the kind of real top flight pro he has in him, and fans are going to have to buckle down and actually show a trace amount of that vanishingly rare Boston sports fan virtue -- actual, genuine PATIENCE -- with the kid while he works his way through it.
Oh, and the other thing we see is that we could score Saltalamacchia for a mid tier prospect. A fairly cheap, efficient acquisition of a young talent with upside is about the best way to go if you want a shot at keeping a good team on the field in the majors without destroying your ability to generate young cost-controlled talent in the minors.
With elite catching being a practically unobtainable commodity, (I can't think of a single current MLB catcher not named Brian McCann who can do all three of Hit, Defend and Stay On The Field) anything someone else has developed is either not going to be available at all, or is going to be nearly as flawed as Salty without half the upside if it is. We got about as close as we could using big market muscle with VMart and it got us exactly nowhere. Going young is the best answer even if it doesn't bear immediate fruit, and if you're going to go young, a once highly touted catching prospect that is still on the young side makes a lot of sense.
What it's going to take to get on the right side of the catching equation again isn't a trade -- that's incredibly unlikely given the state of the farm -- or even a FA signing (any real great quality catcher is going the be the first guy other teams free up money to keep). It's going to take picking up or developing a young talent with some potential, playing them in the major league for a few years -- yes, I said A FEW YEARS -- and letting them learn the business. We're used to being able to take big market shortcuts, and that's a habit we get to unlearn when it comes to catchers, because when it comes to catching those shortcuts tend to either not exist at all or be prohibitively inefficient.