First off, I just want to say wow, what a great job creating this database! Looking forward to following more of this and seeing where you take this.
Second, I have a question of personal interest to me as it's been a project of mine to do a database in this style. I'm currently working on "copying" the Football Manager 23 database (thank God for the editor) to OOTP. As a side note, you can check
this 2020 thread of mine that has Premier League and I think some Championship jerseys if you're interested.
Anyway, my question is: did you mess at all with the Player Development Settings? I have no data on it, but it seems to me like football is a younger sport with a lot of U23 players participating very actively and even being superstars at such a young age. Baseball has moved in this direction lately (see Ronald Acuña, Juan Soto, Vlad Jr, etc.) but it still seems like baseball players develop slower and play for longer than football players. Is this even something you took into account for your playthrough or did you keep these settings at default?