I believe it's much simpler. Francona doesn't prioritize 2024 and beyond.
He thinks that playing the known-quantity veteran gives us the best chance of winning in 2023. Now, you can argue whether that's correct or not, but that discussion still exists outside of this point.
If you say "Hey, we need to see more of these guys so we know what to do in the offseason in order to give you the best chance to win in 2024" then you're probably not getting anywhere because 2024 isn't his top priority. He'll hear that and throw it in the trash bin because it doesn't hold more worth than his status quo of "win games this year"
I'm willing to bet that if you had a talk with him in April and said "Hey, we feel that if you give this young guy a full year of playing time, he's going to be better than Amed by the time the playoffs come around" he'd still dismiss that--because he wants to win games in the present and let the chips fall where they may in the future.