Brown deserved his 2nd team appearance, but that doesn't mean he is a top 10 player. Top 10 season, sure, player, nope. Those are no where near the same thing.
On June 14, the Ringer put out a list of the top 125 for the up coming season, and Brown was not in the top 20. He was 22. They had Tatum at 6 (he was ahead of Luka who was 7, but the other 5 I had they had though a different order). Brown was between Bam and Trae with Edwards and George rounding out the top 25. They had Towns outside the top 30 at 31. Irving came in at 40 (which seems low even for me). Porzingis was the next Celtic at 61 (listed as a wizard). Horford was 67, White 68, Rob 70 (Smart was 71), and Brogdon was 87.
So that list says what I've been saying, the Celtics are very good in the 4-7 range of the roster, but lack a lot of the top end talent that traditionally wins post season series. And for as good as Tatum is, he isn't in that first class of player (at least not yet , if ever).
So Tatum at 6 and Brown at 22. That isn't unreasonable. For Tatum, I am not sure Durant is still better than him, but that is fine. Tatum is 5 to 7 on most bingo cards. That seems fair.
It gets harder to rank say 15-30, there is a lot of parity. I think they did a pretty good job. Brown could easily end up top 20, but call it top 25. How different really is top 20 vs. top 25. Overall, I think they have some of the older players (Kawhi, Durant, Harden, George) all ranked a little high. Maybe Davis and LeBron too. But Brown at 22 is fair enough.
And I am going to make a bold prediction that Porzingis (61) is going to end up closer to Sabonis (20) or Markkanen (28) or even Adebayo (21) than he is to Nic Claxton (59) or Jarrett Allen (63). I understand that he is hard to rank but even if he cracks the top 50, that is still pretty good for your 3rd best player.