If you look at Salty's fangraphs fielding numbers, they are pretty nasty. The poster is trying to make the point that his framing numbers basically makes up for that and I don't buy it.
We get to see Salty play so it is not like we have to look at the stats in a vacuum. He could be in the top 5 for catchers in framing and if he still let balls get past him like those two in Seattle I would still have issue with his defensive skill set.
Catchers age pretty quickly as well so 27 is not as young for a catcher as it is for another position player.
He is improving but big moment plays for a catcher generally involve something around home plate where runs are scored and he will have to improve a great deal there at least in my estimation for me think he is not a defensive liability as a catcher.
In addition in truth the worst thing you can do with stats is try to mix stat processing from two different systems. You cannot take one statisticians processing of something like framing data and mix it with another statisticians processing of other fielding data and come up with a composite answer that means anything. It just does not work as they are not weighting the same, not using the same formulas, it just does not work.
It might work for fangraphs to develop a view of framing and add it to their data for catchers but until then what the poster is trying to do is frankly meaningless.