Tatum isn't really that much of an outlier when it comes to top 3 prospects.
Tatum is top 5 in the 3 point era among rookies age 20 or younger in terms of WS/48.
He's an extreme outlier.
His rookie season so far is up there with all-time greats in terms of contributing to wins for a good team.
Top Rookie 20 years old or younger since 1981 (3 point era), minimum 20 games, 18 mpg, by WS/48:
1. Nikola Jokic, age 20
2. Jayson Tatum, age 19
3. Magic Johnson, age 20
4. Chris Paul, age 20
5. Andre Drummond, age 19
Note that Win Shares per 48 is heavily weighted toward big men, so Jokic & Drummond are probably a bit overrated on this list.
The most recent player comparable to Tatum who had an impact on winning like this is Kawhi Leonard in 2012, and he was only playing 20 minutes a night, whereas Tatum is playing 31 a night.
Kawhi, Magic, Chris Paul .... that's super elite company when we're talking about rookie season impact.