It was never really a question as to whether Francisco Mejía could hit, for a catcher. He can hit, and he’s started off the season well with zero strikeouts in his first 13 PAs, and a visibly quick bat.
The question is how good of a defensive catcher he’s able to become, and whether he will hit well enough to cancel out any defensive shortcomings.
Ever since Mike Fast’s 2011 work to quantify catcher framing — the ability of a catcher to receive the pitch in such a way so that the umpire is more likely to call it a strike — we’ve known that framing is the most important aspect of catcher defense, generally outpacing blocking and throwing by an order of magnitude, so as we get to know Mejía, we should pay special attention to how he receives the ball.