I read an article in the Athletic from three voters for the All-NBA teams, and it seems like they all either had Tatum as last man on / first man off their All-NBA First Team, with Anthony Edwards being the primary competition.
I personally don't see this as a debate. I think Tatum has been better, and he's on a better team. He deserves the recognition.
Basic stats:
Tatum: 27.2 points, 8.3 rebounds, 4.9 assists, 1.0 steals, 0.6 blocks, 47.4% FG%, 38.0% 3PT%, .555 eFG%, 2.6 turnovers
Edwards: 26.1 points, 5.6 rebounds, 5.0 assists, 1.3 steals, 0.6 blocks, 46.3% FG%, 36.3% 3PT%, .524 eFG%, 3.1 turnovers
Tatum also leads in advanced metrics like VORP and BPM (neither of which I'm a huge fan of, but whatever), along with WS, WS/48, and PER (ditto). Tatum has a lower usage.
So, what's the argument? It seems like the only area Edwards is "better" is that his team has overachieved more; the Twolves have already added 9 more wins than last year, while the Celtics so far have only added two extra wins.