Not necessarily. I think after 60 games, you get the roster spot.
After every game, there's a post game stat sheet that lets you know who's getting the most minutes and what their roles are. Here you'll see that you start as a prospect, your minute bar all the way to the left. As you play, and complete the goals, your minute bar fills up and your role does as well. I went from Peospect, to sixth man to starter.. Never landed on bench warmer.
If you see that you're getting more minutes every game, you're well on your way to become a starter.
Try getting A's and A+'s. The coach will call you into his office, telling you he's enjoying your level of play, to keep it up for more minutes.
I thought my game was glitched because I saw this cutscene, in different scenarios, almost every game I got an A and above, until I finally got the starting spot.
Getting an A+ almost definitely needs 7 min quarters minimum on Superstar, for me.
Good luck