My definition of superstar is any player who everyone expects to have a .900+ OPS bat going into the year. I'm guessing that checks out to basically 10-15 guys across the league in any given year. Acuna, Harper, Schwarber, Judge, Alvarez, Soto, and so on.
There are a ton of very good hitters, the Cubs have several of them, but there's a noticeable difference between a guy like Michael Busch and a guy like Bryce Harper. If the Cubs win the WS this year I don't think anyone is calling Michael Busch a superstar if he goes back to a low .800 OPS or high .700 something OPS next year. It's got to be year-over-year dominance.