It depends how you define one-year wonder. As a 5+ WAR guy, I think it highly likely he is a one-year wonder. If you mean can he match the 2+ WAR season of 2023, I'd say the odds are in his favor of doing that at least twice in the next 3 seasons. But, he will be valued as a 5 WAR player and cost us a lot. And... he would mainly replace Schwarber, who has been a consistent 3.5 WAR guy for us last season and hasn't been less than 38 HRs in his time in Philly, and whom we already have under contract for next year.
As for Castellanos, I invite you to explore his splits. During his time in Philly, he hasn't hit at all well at night or against RHP -- really down since his good years. He still hits well enough against LHP and in day games. I think it is management malpractice to start him in a night game against a RHP. At this point in his career, looking at all 3 seasons in Philly, he really shouldn't be a full-time RF. Starting 162 games last season was ludicrous. .