Luck is a funny word in statistics. It does not quite mean what you think it means. It is more of a combination of randomness and 'stuff we don't know how to quantify.' In the emergence of soccer analytics 'luck' is probably a large chunk. Strong correlations are still in the discovery phase. For the Seattle Sounders and MLS luck can sway a couple of results so that a team on the table is not decent, but bad.
If one were to look at ELO based measures of team quality (let's use Sagarin) Seattle looks really good. There's a problem with this in that these measures use some level of data from last season. With the state of turnover in the league does it make sense that a team like Portland is held back because of what Spencer/Wilkinson did? No. So Sagarin does not show that Seattle was unlucky, yet. In about a month more that data will fade.
But where we can see, based on the data from this young season only, that the Sounders results are unlucky is from the work at Tempo-Free Soccer. Seattle is the 4th unluckiest team. Oddly the most unlucky team is the one they rate first overall - the Galaxy.
There's other neat tidbits in their recent update. The Sounders are expected to have another goal and maybe have given up one less (that's where the luck number comes from basically.) But deeper is what Tempo-Free is all about - possessions. Their definition is different. It is about passing sequences before a turnover or a shot. For the people who say that Seattle is not an effective possession team the numbers don't match the theory.
The Sounders are in fact second in the league for possessions per game (remember this is total passing sequences) and fifth for passes per possession. You may quibble about the type of passes/possessions, but not that they exist. Their presentation also shows the most significant problem with the offense - shots on goal. Much of that is likely due to how many Seattle takes from outside the box. The club puts up slightly better than league average shot attempts, but is a dire 16th when it comes to shots that challenge a keeper. By rule shots from outside the box are roughly one-fourth as effective as shots from inside the area.
Liviu pointed it out in the tactical analysis, but look at his chart again.
If this club wants to turn luck into their favor the barrage from outside needs to stop so that the numbers start to favor the team and the pressure is on the keeper to make stops. Even nudging the On Goal number to 3 per match puts Seattle at just under a league average offense with a stellar defense and that's good enough for the Playoffs in any year.
Of course, these numbers are about to change again. Different lineups will appear with the return to health of Evans and Joseph and the return from national duty for Martins, Johnson and Martinez and that may be the biggest offensive boost of all. That won't change that the players bombing from outside need to be better in their choices though.
A little luck going the "right way" would shift the expected goal numbers significantly and the Sounders would be an average team at the start rather than the third worst in the league.