Hey friend, I just had a great idea for your game today randomly (possibly scope creep but what's life without it lol) a way to solve your most requested feedback (the progression spine) you should add tournaments or events the player can sign up for/or automatically happen and it would be wave based battling to test the players collection and the day to day battles can be to hone their skills for better and better tourneys.
I'm not going to try to give specifics. Honestly, I think with your current scope art and gameplay I think you could release a fairly popular paid itch and steam game already with a bit of polish and trial and error based on large amounts of feedback. biggest thing is getting loads of validation through playtesters and change what is most requested.
