I don't assume no significance. I said little evidence.
Given the small sample size and lack of supporting data. I don't think there is any way to draw the conclusion that getting close to 60% is in any way optimal. We can say with certainty that is NOT common as less than 14% of the teams go over 55% which works out to 4.5 teams/year on average with even less teams near the 60% mark.
The .3 win difference between the segment up to 59% and the next lower segment up to 55% seems meaningless given that we are still talking about slightly above average win totals. In the 56-59% range, average wins are only 9.2. That means there were a lot of average to below-average teams in that range. I realize that we don't have the distributions, but unless they are way off the bell curve that seems like a pretty safe statement
What the data does show somewhat clearly is that top heavy teams at 60%+ are not good teams - as in really bad teams
Since there is a HUGE drop off from 56-59% to 60%+, I would bet that within the 56-59% range the that win totals go down as 59% is approached and that the real sweat spot is in in the 54-57% range.
