I would assume the create a team would basically just pull the creator from Diamond Dynasty. It would be silly to me not to just use that as it is already in the game, and while it is a bit frustrating to use, decent once you get the hang of it.
I do agree with the premade MLB looking stadiums. I hope I am wrong and they have a full blown Create a Stadium but that seems highly unlikely to me as a feature for 2020 - perhaps MLB The Show 21.
Either way im excited to have any sort of relocation in the game.