He's a 3, but I agree that he's a future Celtic. He's AWESOME
And what about Jaylen Brown?
Long term, I think Jackson/Tatum and Brown could start as interchangable 3/4.
By the time the C's are ready for that, they will need to have found a great rebounding center. Horford, Jackson and Brown doesn't provide near enough rebounding, but man would they be a problem in every other facet.
In the Jackson/Brown pairing I would expect Brown to guard the 4. Brown is 220 as a 20 year old rookie, he could easily be 230-240 when his body fills out. That is plenty of heft to guard opposing 4's.
The NBA is moving towards every player having the ability to play on the perimeter, you don't really have to worry about bigger 4's destroying smaller 4's in the post because that is not the way the league is being played.
Once Jackson and Tatum fill out, both should be able to play the 3 and the 4. Height and girth at the 4 has become secondary to shooting and defensive versatility. It's not like Jackson or Brown would be counted upon to be the primary rim protector/rebounder at the 4.
People get waaaaaay too hung up on positional archetypes. The modern NBA is all about defensive versatility, and less about each position having a specific role.
The Celtics run a lot of their offense through their 4/5, their 2 is their best rebounder and every position on the court is a threat from 3. Why do people hold onto their preconceived notion of what each position is supposed to do rather than pay attention to how the game is currently being played.