I went ahead and watched highlights of Pascal Siakam's 44 point game last night against the Wizards.
As I did, I kept thinking:
"Man, if Siakam can make this kind of leap and have this sort of game at age 24-25, imagine what Tatum could do."
Seeing what Paul George has done this year is also instructive w/ regard to Tatum.
That said, the biggest difference between George / Siakam and Tatum is that those guys have been defensive menaces since they entered the league.
Siakam especially has a tough guy / mean streak to his game. Whereas Tatum plays more like the "smooth assassin" archetype along the lines of Kyrie or KD.
Seems to me that for Tatum to become more than just a supporting All-Star scorer, he will have to unlock a physical element to his game on both ends.
Otherwise he would have to add a lot of point guard skills to his game so that he can run pick and roll and create offense for others. That seems like a huge stretch based on what we've seen so far.