He had more success, sure. I just don't see his career trending back up. Even the 2018 Herrera was below-average offensively (94 OPS+) and didn't compensate with defense.
Sure, if you could actually throw him out there every day in the big leagues you'd at least get to find out, but there's little reason to think the player we saw the last two seasons, with 4 months of not playing baseball to boot, will ever be what he was when he was 25. Just like Franco and Hernandez.
Kingery is our third-best option in CF, if Haseley got hurt that is what they would do, and if Quinn got hurt he'd probably turn up there once or twice a week too. And they'd absolutely put another utility guy out there (whether at 3B or CF) before considering Herrera. Probably two (i.e. they will call up Martini, assuming he's not already on the 26).
Sean Rodriguez in 2019 was not demonstrably worse than Herrera in 2018 (especially with that .348 OBP). Maybe Herrera (like Rodriguez and Miller) would do better in a platoon/bench role too but with Williams also in the mix he won't get that chance (should Bruce be injured) either.
Ironically, Herrera's career is (potentially) ending as a mirror-image of how it began. He broke out with the Phillies because the rules granted him a certain opportunity if he wasn't on the Rangers' 40. Now he will be unable to pursue any opportunities because the Phillies are paying him $20 million to not be on their 40.
I like the guy and would like to see him put it together (assuming he's not a truly toxic person), but that's only going to happen, IMO, if the Phillies release him, not if they keep him around as their 5th-string CF in hopes of getting some team to buy him from us for $2 million.