Right off the bat, there are a few candidates that can be eliminated due to a lack of defensive abilities. These are Gary Sanchez and Mitch Garver. Both were two of the most productive catchers offensively, swatting 65 home runs and combining for a .918 OPS between the two of them. They were on the two most powerful offenses in MLB history.
However, their defense prevents them from being considered the best in the league. Gary Sanchez’s defensive struggles have been well documented. While he improved, he still struggled to block and frame in 2019. According to Fangraphs, he posted a -6.8 FRM and -2 DRS. Garver was better at blocking and framing, but lacked elite arm abilities. He had a 16.2% throwout rate, and a -2 rSB, which calculates runs saved by preventing stolen bases. While they were elite sluggers, they were not elite defenders compared to the rest of the field.
Next to be eliminated are the catchers who excelled defensively, but did not do enough offensively. Roberto Pérez and Christian Vazquez would fall into this category. Both have been known as defense-first catchers throughout their careers, but are coming off their best offensive seasons. However, their defense did not suffer as a consequence of their increased offensive production. Pérez continued to be one of the best defensive catchers in baseball, posting an insane 29 DRS and 9.8 FRM on his way to his first career Gold Glove. Vázquez was great too with an incredible .999 fielding percentage and 12.4 FRM.
While their offense was greatly improved, it was still not good enough to compete with the other candidates on the ballot. Both Vazquez and Perez were valuable hitters to their team, but still struggled with strikeouts. As a result, they posted offensive WARs of -3.1 and -5.2 respectively.