It's a combination of factors.
Age, position, experience, performance, health, projected production are some of the important ingredients in the gumbo.
Another one -- team performance -- also factors in, whether that's fair to the individual or not.
You brought up Molina, and that's a great one to look at. He debuted at age 21 in 2004. If you go by adjusted on-base plus slugging percentage (OPS+) he did not have an above-average offensive season until his age-28 season in 2011 produced an OPS+ of 124. Molina was a three-time All-Star by that season's end. His dominant defense was his biggest strength, and everyone knew it. And he lineup he was a part of tended to support his shortcomings on offense until they were no longer shortcomings.
Bader debuted at age 23 in 2017. Two of his four seasons, 2018 and 2020, have produced an above-average OPS+ of 106 (2018) and 111 (2020). His 2017 season was 32 games. His 2019 season was disappointing (OPS+ of 80), but he seemed to get little to no credit from some for building off of that to have a better 2020 season.
I won't go as far as comparing the importance of Bader's defense to Molina's, but there's no question he has the potential to be a Gold Glove winning center fielder, a position where elite defense means more than any other outfield position. If you sacrifice some offense to achieve that, no huge problem -- IF you get the offense out of the corner outfield positions. That's been Bader's problem as much as his hitting ups and downs -- he's in an outfield that has not produced well enough to support an elite defensive center fielder who is figuring it out at the plate.
I think his defense will probably always be better than his offense, but I am not ready to say we know everything about his offense yet. We also don't know if the Cardinals can come up with the kind of outfield that can produce a glove-first center fielder. It has not since Bader has been on the scene. He needs to be more consistent, but he would also benefit from playing in an outfield that incudes some more consistent threats offensively.