Send down to Triple-A to get everyday at-bats and improve vs. right-handed pitching
Dylan Carlson is still a very valuable asset for the Cardinals. At worst, he's a good defensive outfielder who can rake against left-handed pitching. That is a valuable player in today's game, but the Cardinals should be helping Carlson become more than that.
The glaring hole in Carlson's game is the ability to hit right-handed pitching. Despite making major adjustments this offseason, Carlson is slashing .194/.256/.278 in 39 PA against right-handers. What's even more concerning is that this is what he has been his entire Major League career. In 972 PA, he's slashing .224/.305/.375.
Right now, the Cardinals rightfully do not trust Carlson against right-handed pitching, which has basically relegated him to starting against left-handers, pinch hitting late in games against southpaws, and coming in as a defensive sub. That's not a wise use of a 24 year old outfielder with so much more potential than that.
I'm not saying Carlson needs to be in the Cardinals' long-term outfield, but if they want him to have a chance to stick in center field for them, or be a valuable trade asset, the best thing for him is to go down to Memphis and figure things out at the plate.
If Carlson can even be league-average against right-handers, that's a very valuable player.
I'm sure Carlson wouldn't love the idea of going down to Triple-A, but it's the best thing for him and the club right now. If he continues to sit on the bench most of the time, that's not going to help him fix his major flaw.