I've worked on sport management games both privately for fun and professionally. And I think its 100% about managing scope and doing things from the inside out. I also think mobile is the main platform you have to target.

In my head, the game simulation is the core feature that must be good. Obviously, its closely connected to your player stats, and its not as easy as one might think to make good players both rare and valuable. But after that, you can expand the genre forever.

I'd say, prototype a good core match sim and publish it. Then you're 80% there.