I've been a big supporter of Leon and Vaz, but I have never come near saying they are the best defensively. I have often acknowledged there are better catcher while warning of a possible learning curve, if we made a switch.
I'd say Leon & Vaz are top 10 or 15 out of 60 catchers on defense (individually & combined) and bottom 10-15 on offense (combined).
Of course there are catchers out there that can do what they do on defense AND hit better or much better, but it's not realistic to think we should spend our limited resources trying to upgrade the catcher position, when who we got work fine as is and are a net plus overall.
Yes, Sale was great before coming here, and putting up a 2.51 ERA with AJ Pierzynski supports your point, but the guy he has had the most PAs against with is Tyler Flowers. Here's a look at the CERAs:
2.42 Leon (319 PAs)
2.51 AJ P (226)
2.98 Navarr0 (just 97)
3.02 Flowers (552)
3.36 Phegley (just 88)
3.40 Vaz (just 53)
3.53 Avila (112)
4.08 Navarez (just 18)
David Price is clearly had to re-invent himself, so I'm not sure it's fair to compare his numbers with TB vs BOS. I know it sound contradictory to say the catcher makes a huge difference, then selectively negate the theory when it suits my position, but I think I have a good reason.
Price also had one of the greatest defensive catchers of all time, Jose Molina. for the plurality of his PAs against, yet Leon still matched Molina and beat almost everyone else who had over 500 PAs with him. Here's his numbers:
2.83 SLeon (769)
2.85 JMolina (1878 PAs)
3.06 JJaso (778)
3.09 Navarro (542)
3.61 Shoppach (675)
4.32 Vazquez (1113)
(Avila, McCann & Martin all got sub 3.00 with Price with between 296 and 451 PAs with him)
I'd be thrilled, if we found a catcher like Leon who could hit, but unless we draft one, we can't afford to buy or trade for one, right now.
I view Vaz/Leon as a clear net plus, but they certainly are not great or top 5 or 10 in overall value out of the 60 catchers who see the most time behind the plate.