If you built more around Tatum he could be a top 20 player as a SF.
I don't see him as a top 5 PF as rebounding, defense and shooting fg% is usually a big thing in judging PFs. I like Collins, Giannis, Davis, Siakam, Green, and Markkanen ahead of Tatum as a PF. Gordon, Griffin and Randle could be argued as better PFs as far as skill sets asked from the position as well.
Nothing is set is stone not saying it can't change.