4. Swiss army knife
The biggest advantage Simmons has over Tatum and Mitchelle can be seen by simply looking at a stat sheet.
Tatum and Mitchell are scorers. They are very good offensive players, especially for their ages, but that is their main attribute.
Simmons is a stat sheet stuffer. He scores, rebounds and, of course, passes the ball. When you do all three well in a game, the result is a triple-double. Most rookies do not enter the NBA with that well-rounded of a game.
Simmons finished the season with 11 triple-doubles, knocking Magic Johnson out of second place all-time for rookies (he had eight and then led the Lakers to the NBA title). Only Oscar Robertson, thought of as one of the greatest guards of all-time, had more. Robertson, known as Mr. Triple Double, came into the league after spending four years in college (to one for Simmons).
Neither Tatum or Mitchell had a triple-double, something even a shot-challenged Markelle Fultz was able to accomplish.
When it comes to being an all-around player, Simmons gets the nod.