LeBron, Curry, or Durant all got a pretty good amount of minutes in their debut season in the NBA. Meanwhile, Jokic and Giannis got relatively limited minutes in their first season, but that didn't stop them from becoming great players. I mean, even if Flagg gets a few minutes in his first season, it doesn't mean he won't become an all-star player in the following seasons.
Lebron did, but Curry really wasn't who he was at the rookie season neither, he just played at the position because of injuries and all that, I remember back when Baron Davis was their point guard. Flagg could play, because they do not have many more neither, Doncic did too, because they didn't had anyone else.
Curry's rookie season is 2009, Baron Davis was a Warrior till 2008, so they didn't crossed path. Maybe what you meant is Monta Ellis. Yes he was that flashy point guard that they had but they eventually traded him and keep Curry.
So when a player plays a lot on their rookie season, not because they are already great, but because the team has nobody better, that results with plenty of minutes but the player is not great yet. But that's great, because first year being great minutes, equals second year being easier, and then fourth year is when they start to peak and get better. So cooper has 4 seasons, and after 4 seasons, he will show the world what kind of star he will be or he won't be.
We will have to see what is their plan on Cooper Flag. Mavs have a lot of good players, with AD at the helm. So I doubt that the Mavs will just rush him to be a big star in replacement of Luka. What I'm seeing is that maybe a good 20-30 minutes per game type of play for him. Unless he really had this big games consistently that he will be in the floor and log a lot of minutes like Wemby before.