Loved reading this! I've also been making a Digimon TTRPG for a few years after being disheartened by the lack of good existing ones (like, come on, do we need tactical, grid-based combat for Digimon).
I'm really curious to see what this design would look like after you came in contact with PbtA, like you said in the foreword. One thing I love, that I also ended up arriving at, is having the players take charge of both a digidestined and a partner digimon. I think that could be a lot of fun at the table.