Personally I'd argue that Jayson Tatum is already an NBA "superstar," based on all his 50 point games and performance so far. If you have a stricter definition of superstar where you require a player to have All-NBA 1st or 2nd team selections under their belt and more team success as the unquestioned star of your team, I can understand how you don't have him listed as a superstar right now.
Maybe your list is just LeBron, Curry, Giannis, and Durant for all I know, so it's open to interpretation. One thing I do know is that we need Tatum to make the jump to the "Practically everyone says he's a superstar" level for the Celtics to compete for a title.