I mean, they get to coast because they are in the East
IMO, BOS would be the 2 seed in either conference. . . and could have done so by coasting some of the time. They have a .745 winning % against the East and a .724 winning % against the West. At that rate, Giving them 52 games against the West instead of 30, they would still end the season with 60 wins. That would put them 10 games up on HOU. The C's goal for the regular season was to end the season healthy, keep guys fresh, and give some non-starters more minutes to grow and develop. The real season starts in a few weeks.
I expect one thing may come into play for teams like CLE or OKC. Their guys don't have much experience playing an extended season and playing a lot more games in a deep playoff run. The Celtics have multiple guys that are used to playing a lot of games with deep runs . . . Tatum (had years playing 100, 99, 94, 93, 88, 85 games), White (102, 98, 92), Brown (95, 90, 89, 88, 87), Horford (92, 92, 91, 89, 86), Holiday (90, 88) . . . even reserves have seen a lot of time Prichard (101, 95), Hauser (98).
I remember seeing an interview with Donovan Mitchell after the Cavs lost to the Celtics last year. He said one of the issues by the end of the year was fatigue. They gave 110% in every game and every practice. They had something to prove and wanted to win every game. There motto was play hard for 48 minutes, no matter what the score or situation was. But he admitted that by the end of the season, they were drained, and that mindset actually wore them down. Jumping ahead to this season, Mitchell has already played 10% more minutes than last year with 6 games to go (will end up with 15-20% more minutes played unless they sit him). I don't think he's stopped giving 110%.
The point being, for CLE to win series after series in the post season, they will have to play in a lot more games than their players are used to. Obviously, the Thunder have been spectacular and are a young team. But they don't have guys that have gutted out 90, 95, 100 games in a season. Maybe that matters, maybe it won't. But it certainly could be a factor. How much? Who knows?