I think Tatum could be top 10 in the coming season. I don't think he has shown it yet though, people saying he's top 10 are projecting that by excusing his post-COVID period, and combining his best offensive periods with best defensive periods.
I also think we need to see him both show the level of offense he showed in bursts this season AND the level of defense he showed in previous years, because at no point last year did I think I saw an elite defender and an elite scorer at the same time (pre-COVID included) and (yes he got COVID) he has never shown a full season of consistent top level play. The hardest thing for an NBA star is to sustain top level performance at both ends across a full season. I get the argument that the overall defense was struggling, but he was part of the issue for sure, and elite defenders show more even on teams struggling with system-wide D.
Keeping both of those up at the same time is the hardest thing in the NBA, you can't just assume it, a lot of players take a step down defensively as they grow into elite players. If Tatum can consistently be a high impact player on both ends he's top 10, but if he is only high impact on offense and lower impact on D like last year he's probably more in the 11-20 range of players.
I would say based on current performance Tatum is behind:
Jokic, Embiid, Durant, Harden, Giannis, Curry, Luka, Kawhi, PG, Lebron (yes he gets hurt, he's alsobetter than Tatum when healthy, and Tatum hasn't put up a full season of elite play either).
I'd put Tatum currently in the next tier with Gobert, CP3, Kyrie, AD, Mitchell, Butler, Trae
If I were guessing, I'd say Tatum goes to the tier above next year. He can be PG-lite on D, but better on O, which would separate him from the guys he's in a tier with now, while Kawhi and LeBron are health decline candidates (Curry and Harden too).