What are you even talking about with this? There is only one guy who can only play 3b (Devers). Everyone else that can play 3b, can also back up at other positions.
https://www.upi.com/Archives/1987/07/17/Mike-Greenwell-forced-to-make-his-major-league-catching/9890553492800/
Would he be better or worse than Mike Greenwell at catching?