Moreno is better at throwing out runners and controlling the running game, but Kirk is better at blocking and framing. I think it's far from a slam dunk that Moreno is a better overall defender at this point but I do think he has a higher overall defensive ceiling due to his athleticism.
Baseball prospectus has a detailed catching defense leaderboard which takes into account framing, blocking and stolen base prevention. Kirk is ranked 13th in catcher defense added, vs Moreno who finds himself way down the board in 77th place.
https://www.baseballprospectus.com/leaderboards/fielding/