I am not sold on Marsh being plus defensively. He has decent speed and range for an outfielder, but among the subset of legit center-fielders it is much more average. And we have seen the mistakes. Obviously like any young fielder he can get better in that respect, Defensive stats are variable of course, but for 3 years in a row he has been average at best in CF. Plus in LF but very average or a little below in CF.
I do agree that there is some untapped potential in the bat that was not realized in California. But I also see O'Hoppe's offensive potential as even higher. In 2021 he had a BB/K ratio of 33/76. In 2022 that improved to 70/74 with more BBs than Ks at his last stop. That is extraordinary. Marsh has a major league ratio of 27/154. It is 5/37 with the Phillies. The K rate has improved but so has his BABIP (from a high .341 to a skyhigh .386).
It really looks like the biggest change in Marsh with the Phillies is his increased aggressiveness. His BB rate has dropped along with the K rate. There just is not evidence he is a much better hitter yet. Hopefully he can adjust to seeing less strikes in the future, because that will happen if he keeps swinging early in the count.