I would trade Mancini and Santander if the return is fair (debatable I know). Neither is going to be a contributor on the contending 2023 team. Go into 2022 with Hays, Mullins, McKenna, and Robert Neustrom or a cheap free agent signing/trade acquisition. Jorge Mateo and Jahmai Jones can play outfield too.
The outfield depth is coming. I think Stowers can be at least the strong side of a platoon with Hays or whoever. But you also have Neustrom, Diaz, Zach Watson, Johnny Rizer, Hudson Haskin, Colton Cowser, etc, etc.
I just think you can fairly easily replace the production they provide and get something for them in the process.