The thing that doesn’t feel right about comparing Tatum to Paul Pierce is, if I remember correctly, when Pierce was drafted, his defense was considered his greatest strength, with the potential existing for him to become a great scorer. These qualities seem reversed in Tatum’s case.
Either way, I think this article outlines the risks and rewards of Tatum vs. Jackson. With Tatum, your best case is Carmelo Anthony and your worst case is someone like Evan Turner. With Jackson, your best case is Kawhi Leonard and your worst case is someone like Jerami Grant.