Or maybe it is that Tatum and Brown aren't good enough coupled with a terrible supporting cast. I mean aside from Young, the other 3 guys are all clearly better than Tatum and Brown. Additionally, who is the 2nd player on those teams currently? I'm pretty confident every single one of us would take Brown over Westbrook, Harris, Gordon, and Collins. So why is it that Boston with 2 all star level players can't win? Maybe just maybe it is the 2 all stars that quite simply aren't good enough. And perhaps they aren't good enough because they don't maximize each other's ability, which is why you see people like me, saying the team should trade Brown for better fitting pieces around Tatum.
Those 4 "second fiddles" that you mention all support the most elite, MVP level players; LeBron, Embiid, Jokic, and to some extent Young. It is true that Tatum is not currently as impactful as LeBron, Embiid, and Jokic (I would put Tatum over Young). So what does it prove that Tatum is not as impactful as LeBron?
And yes, Brown is better than Westbrook, Harris, Gordon, and Collins. If you were going to try and win a championship this year, would you take LeBron + Westbrook or Tatum + Brown? What does that prove?
Memphis is winning with a big 2 of Morant and Jackson. Phoenix with Booker and Paul. Utah with Mitchell and Gobert Are they better than Tatum and Brown? Or is the difference the 3-15 players?
Another key point in my mind is that most of these key "big 2" combinations include at least one really good big. My theory is that the problem with the Celtics is not Tatum and Brown but rather Horford, Williams, and Williams.
Most of the top teams are a combination of a top big and a top wing. A few has a PG as one of the top 2 but most don't. I guess the ideal combination would be to have your best player be a wing and then 2/3 be a big and a PG. That would be total balance. That is PHO (wing-PG-big). But the defending champions has a big as the best player with probably the PG as number 2 and then a wing. The Lakers did it in 2020 with LeBron (kind of a big), Davis (a true big) and then really no clear #3 (Schroeder?).