NBA rookies becoming legit superstars upon entering the league is a rarity. Most rookies are, in fact, net negatives for their teams. Rarely do rookie resemble the superstars they are projected to be immediately upon entering the league. It's a testament to the skill level of the NBA and the real superstar qualities of the players who do, in fact, make the leap and are instantaneously productive.
Karl-Anthony Towns (excluding last night) and Kristaps Porzingis are to date playing at a value level far and above what most rookies, even number one picks and some all time greats, have as rookies.