I mean for me, it IS boring. The level of skill isn't there, so it's boring to watch. The atmosphere for most teams isn't there (yes, yes Sounders, Union), so it's boring to be there or its boring to watch it on TV. I mean, this year's MLS Cup final was an absolute yawner, and while there may be some exciting games throughout the season...for the most part I don't care much for it.
Yes, MLS' schedule doesn't interfere with the majority of European leagues, but....Gold Cup, European Cup, Copa America, Confederations Cup, the tournament in the summer Olympics...there are better events to watch in the summer (usually).
The only reason why MLS is able to have varied winners is thanks to the playoffs system.
While I may enjoy it when a team that doesn't do so well in the regular season being able to enter the playoffs and maybe go on to win the whole thing in other sports like Football and Baseball, I don't care for it all in soccer. If you want varied, then watch Champions League! As far as I can remember, no team (in recent history at least) has won the title back to back.
In Spain, the top two teams are always the winner, but they're a long way off from being like Scotland. I mean, other than Celtic and Rangers, most of the other teams in SPL are not quality at all. I would say that the top teams in MLS would probably be competitive in the SPL, at least more competitive than they would be in Spain.
In Spain, teams other than the top 2 have been in the Champions League, and they've been successful in the UEFA Cup/Europa League. There's a reason why more Spanish teams qualify for the Champions League (and Europa League/UEFA Cup) than the Scottish teams.