I reckon Andrew Knapp has a job because they are happy with his defensive/pitcher-handling work overall, plus he's a switch-hitter on a short bench who is an adequate pinch-hitter (a .221 BA being about average, I believe) and rarely plays given how much work Realmuto gets. Doesn't mean his offense has been acceptable, because for that kind of production you can probably have at least a minor defensive upgrade (especially since none of the pitchers Knapp supposedly had a rapport with even stuck in the rotation permanently), but the grass isn't always greener. Of course if Grullon is ready, and given the possiblity of a five-man bench, his time is probably done. You could definitely do worse than to keep him in AAA if they are ready to have three catchers on the 40.