It's correlates when the best player is on a team with supporting talent that's not wildly divergent from the supporting talent of their comparable peer on the other team.
Kareem was the best player going into pretty much every series he played in the 70s, and he won one title during that decade.
Jordan was the best player in every single Bulls-Pistons series (meaningfully different supporting casts to Isiah or Dumars), and he went 1-3 overall.
It's very possible and maybe even likely whatever team you place across from these Celtics wouldn't be "more or less" neutralizing the "others". The 3-9 spots in the rotation *radically* favor the Celtics (best bench +/- in the league, almost 2xing the next set of teams).
Hitting 17 threes a game on nearly 39 percent is a super premium. The bench hit at the exact same rate as the starters as well.
Edit: It's one thing to have the best bench in the league (the Celtics were ranked 1 in bench +/- at 3.2 IIRC)...but it's another thing to have the best bench stacked *on top of* the best starters in the NBA (the Celtics were ranked 1 in starters +/- at like 7.5 or so).