When both Patrick Bailey and Matt Chapman are in the lineup, the SF Giants have about as good of a defensive alignment that they can have at catcher and third base, respectively. In fact, both players lead baseball in Defensive Runs Saved (DRS) at their respective position.
Pair of SF Giants players lead in key defensive metric at their respective position
Hat tip to SIS Baseball for illustrating that point. Bailey leads all catchers with +18 DRS, whereas Chapman is the best third baseman in that category with +15 DRS.
Cal Raleigh (+17 DRS) of the Seattle Mariners is right behind Bailey for the league lead. However, Chapman has a pretty comfortable lead at the hot corner. Ernie Clement (+11 DRS) of the Toronto Blue Jays is next in line at third base.
Of course, this probably confirms what you have already seen from both players at their respective positions. Chapman covers a lot of territory and has an excellent arm. On many plays, he takes some of the pressure off of the shotstop with how much range he covers. Chapman makes plays that you just do not see many third basemen make.
On the other hand, Bailey is an elite pitch framer with a quick and accurate arm. Giants pitchers have not given him much help in terms of managing the running game, but when given a chance, he likes to show off his arm.
DRS confirms the eye test in both respects. That said, DRS is just one defensive metric. Both still rank as some of the best with other defensive metrics as well. Chapman has registered +7 Outs Above Average (OAA) and +5 Fielding Run Value (FRV), both of which rank second among all third basemen.
On the other hand, Bailey leads all players with +21 FRV. He also leads all catchers with +21.9 Catching Defense Added (CDA) according to Baseball Prospectus. CDA attempts to capture framing, blocking, and throwing into one metric. Given Bailey's excellent framing ability, he ranks highly in this metric.
I realize that this has led us down an analytic rabbit hole. However, it just points out that both Chapman and Bailey have been some of the best defenders in baseball and each one has a strong case for a Gold Glove Award in 2024. Plus, the good news is that the Giants expect both to be with the club for the foreseeable future.