I agree to a point on the Cavs, the regular season and post season are different. But remember that everyone said DEN wasn't a playoff team, many even said BOS was not a playoff team, even right up to the series with DAL. I think CLE is better than a lot of people think. I see both Mitchell and Garland as better than many people think, but BOS is better right now in my mind.
Their rotation is very good at the guard positions and very good at the big positions, but they are kind of barren at the wing positions. That is their weakness. One trade or other acquisition could address that. Mitchell is a very high level scorer. He makes up for the lack of scoring/playmaking from the wing positions. But weaknesses do get exploited more in the playoffs.
Mitchell averaged 29.6 pts in the playoffs last season. Allen was next at 17.0 pts Garland was not 100% and only averaged 15.7 pts. Mitchell averaged about 32 pts vs BOS in the playoffs, on 53% from 3. Of course he only played 3 of 5 games.