Mets catchers not named Travis d'Arnaud are currently batting .197 with a .291 OBP and .283 slugging, which ranks 27th in MLB. They've combined for just nine extra base hits and, while they're drawing walks at a slightly above average rate, it's not enough to overcome their awful batting averages.
For a team ranked 13th in the National League in runs per game, this is a significant concern. Deeper lineups can bury bad catchers in the 8-hole, but there are arguably four other batters on the Mets that should be hitting there too...
Defense is a bit more of a mixed bag.