The disparity between Leon and Vaz is actually greater with Price than Porcello, but for some reason, Vaz has become Price's only catcher. It's working, this year, so I'm not complaining.
Career CERA:
Sale
2.53 Leon
4.61 Vaz
(Vaz would have to go 3 for 4 every game to make up for 2+ runs)
Price
2.75 Leon (0.00 in 2019 but only 6 IP)
4.16 Vaz (3.59 in 2019- 73 IP)
5.73 Swihart
Porcello
4.06 Leon
4.70 Vaz
4.93 Swihart
ERod
4.15 Leon
4.28 Vaz
4.44 Swihart
Some differentials are wider than others, but all show Leon gets better results than Vaz.
An ERA differential of 1-2 runs would take an enormous offensive differential to outweigh that many runs per game. Vaz is doing great on offense, but I doubt a .250-.300 OPS differential equates to 1-2 runs per game.