It might be good to clarify what that means...
That graph means that the win ratios of the top 250 players range from 66% to 79%. On average the top 2v2 players win about 72.5% of the time. So around a 3 to 1 ratio.
yeh sry my bad, should have mentioned that.
And the main thing this stats show is the huge effect on 2v2 from Winter Balance Patch and the GCS Balance Patch (from pretty allies-favored to pretty axis-favored) that have been released in late March + early April 2017