Tatum was 4th last season, quite a bit behind Embiid, Jokic, Giannis, and quite a bit ahead of Gilgeous-Alexander and Mitchell. Embiid is obviously not in the running this season due to games played. I see worst case, Tatum stays 4th (SGA moves up), but best case, arguments could be made for Jokic or Tatum with Giannis dropping down. I personally see Tatum as ahead of SGA and Mitchell, also probably ahead of Giannis this season.
But this is not what I am focusing on and I doubt Tatum is either. The real prize is finals MVP. That will do more for Tatum's legacy than the season MVP.
It is not a knock on a player to say he should be anywhere in the top 4 in the MVP voting. Tatum may not ever be the outright best player in the league in a season. But he is going to be in the top 3 or 4 or 5, at least every season for the next several. I'll take that.
I'm curious, why do you have him over SGA? I don't think it's debatable that SGA has been better. Is it simply the "best player on the best team" argument?
Yes, I believe some MVP "points" should be awarded for team success, not the end all, just a part of the equation, and Tatum is the best player on a better team. I think it is debatable as to whether SGA has been better, or more valuable based on individual production. Yes, he averages about 4 more points (about 15% more than Tatum), but Tatum get more rebounds (over 50% more), and plays better defense. SGA gets more assists but probably has higher usage (in my mind, assists can be a deceptive stat). I think it is a fair debate, I like Tatum a little better, others may see it differently, but to say it isn't even debatable, in my mind is going too far. I like Tatum better, but accept that it is close enough for legitimate debate.
As to Mitchell, I agree he is really good. He would likely be right there with in the debate with Tatum and SGA, if he had more games. But he doesn't this season so I have him behind both. He has 47 games, CLE has 20 remaining. If he does get to 65, it will be just barely. In any case, I think he has been less valuable because of games played. Maybe that isn't how you are supposed to score, but that is how it is in my mind.