The NFL works very well because they play so few games, and only 12 teams make the playoffs. The amount at stake in each week of the regular season is much higher than in any other major sport - almost immeasurably higher than the MLS regular season. And, in the playoffs, the best teams play one less game which offers a significant advantage.

MLB's regular season is too long, IMO, but their playoff format is pretty balanced and fair. Generally speaking, the best teams go the furthest because you have to win a multi-game series.

I think MLS has the worst of both worlds. Their regular season is long, undramatic, and only sort of meaningful. The playoffs are currently unbalanced and aren't really resulting in the best teams winning.