I think it's already been proven that what he did in the minors last year, especially in the inflated AAA environment, didn't mean much (and is also a small sample). Ditto spring training. And the the data we have for his six previous seasons doesn't make him look any better even if the career OPS is better than the SSS 2023 OPS.
At 31 I just don't know that he has potential. If he was a truly viable CF then he's a Jankowksi or something. If he was an IF, a Phil Gosselin type. But still basically a AAAA player and depth piece. He made the team last year on merit and then got more chances because Schwarber was already hobbled coming out of the WBC; he also got demoted on merit, and only made the playoff roster because there was literally not another LHB in the system who was better. And so it would be today if the season started tomorrow.
But all of this really gets to the core of the issue doesn't it? When I mentioned that last year's team got by without a fully operational bullpen last year you pointed out that they could have stood to have a better team from Opening Day and won more games by June 2. Playing Cave and Clemens instead of Harper and Hoskins was also part of that. If Marsh were to miss 4-8 weeks of the regular season at any point LF production would be ugly. Pache is your glove guy and 3rd CF, Cave is your bat guy who won't ever actually play CF (even if there's one injury). He needs to have a better bat if so.
He also got nearly 1/3 of his ABs as a 1B last year. So certainly they did prefer him to Clemens in the end - and Darrick Hall too. But I'm still not sure I buy it.