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.
It is fine, but here are the rankings of other top teams (I went through top 66 - so higher than Al)
Top contenders
Den - 1, 16, 45, 62
GS - 2, 34, 46, 48, 56
Mil - 3, 38, 49, 54
Pho - 4, 10, 42, 66
Phi - 5, 19, 55
Bos - 6, 22, 62
If healthy could easily win a title based on top 2
LAC - 8, 25
Mia - 9, 21
LAL - 11, 12
Probably 1 piece away (or need a young guy to take a leap)
Dal - 7, 40
Cle - 15, 35, 36, 64
Sac - 17, 20
Mem - 18, 33, 39
Min - 24, 31, 52
NYC - 26, 43
NO - 29, 30
All of the top contenders have a player ranked higher than Tatum, many have a different player ranked higher than Brown, and all have at least their 3rd player ranked higher than Zinger. And this is the highest Tatum has been ranked and Brown has been in that range for a season or two. So the fact that Boston has over achieved (while a team like the Sixers has under achieved) has clouded judgment on the Celtics nationally.
The thing about all rankings is that they fluctuate so much over the year. When the Ringer started this list in December '22,
this was how Denver's players ranked:
3: Jokic
47: Murray
62: MPJ
74: Gordon
So Boston's 6, 22, 61 (and 67, 68, 87) doesn't look so bad when comparing it to how the reigning champs started their season

Also from
the Ringer's Top 25 ranking (from March '22), we can see how much guys ranking can change in a season (and not talking about young guys who you expect to see big leaps from, or older players who might decline, but guys aged 25-30 who should mostly be known quantities).
Fred VanVleet went from 24 to 51
Zach Lavine went from 22 to 47
Rudy Gobert went from 17 to 52
KAT went from 16 to 31
Trae Young went from 15 to 23
On the flip side, I'd imagine we'd have see big jumps from guys like Sabonis and Brunson if their list last year extended past 25. (The current ranking also shows Julius Randle as a big riser gong from 91 to 43 from when they started the full list). And I'm sure if I went and pulled ESPN or CBS rankers I'd see players with similar big swings year-to-year.
All that to say, fans who are optimistic about guys like Brown and Porzingis, aren't necessarily claiming things that have no basis in reality. Not out of the realm of possibility that Brown could climb 5-10 spots or Porzingis could climb 30 spots if the Celtics have a great year. Happens all the time, every year. The thing that really moves players in these rankers is if your team over/under performs. (They can also all fall down, but here's hoping that doesn't happen).