Shortly after I wrote the initial post I did some research between teams who had Heroic WI and teams that had bad or just OK WI.... and.... I couldn't find anything that would solve the mystery. Over the last week I acquired 3 players. There was nothing special trait-wise about these players, but it has increased my WI to Heroic and subsequently knocked my Teamwork down a few rungs, although still Harmony. So.... I still have no idea.
What I do know is that the two teams facing off in the S3 GHL Finals do not have Heroic WI. One is just OK and the other is Strong, but seems to border more on OK than Heroic. I'm sure WI has an impact, but it seems like having talented players has the most impact on winning and losing.