Baseball Prospectus ranks catchers defensively by framing runs, fielding runs, blocking runs, caught stealing runs, stealing runs, and throwing runs. Out of 117 ranked catchers in 2018, Leon ranked 7th and Vazquez ranked 14th. Swihart ranked 38th, which is not bad out of 117.
As a team, Boston catchers ranked 3rd out of the 30 teams.
Those are based on the measurable stats. I think Leon and Vazquez would rank even better when you factor in the intangibles.
Regardless, don't mess with a good thing.