BI is a better passer, and when he's having his best games, I think he controls pace better as well.
Tatum is by far the superior 3pt shooter (higher percentage, higher volume, higher percentage of self created three, for several years in a row now) and the better defender by a fairly significant margin as well (For comparison, BI DEPM this year was +0.4, 72nd percentile, by far a career high: Tatum's was +1.4, 88th percentile).
Overall I think Tatum is a better player but it's not by a huge amount. Both top 50 players, no doubt about it in my mind.
Edit: put Tatum's overall EPM instead of just his D-EPM, fixed that. Point still stands.