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.
Your comparisons don't have too much merit since you can't really compare number 1 or 2 draft picks (Curry was different) with a no 15 draft pick (Giannis) that was skinny as fk and had a lot to learn or a number 41 draft pick (Joker) where there wasn't a lot of expectation.
High draft picks always get their playing time, especially when they are considered a "generational talent".
Dallas has a good roster and Flagg will fit right in.