Ooh, yeah, this looks fun. Statistical analysis, I choose you!
Mean victory rate is 65.75%, in 511 games. Legacy is 78.45% with 116 games, Tempest is 75.61% with 123 games, Tachyon 74.79 with 119, Young Legacy 74.79 with 31, Visionary 72.58 with 124, Expat 60.36 with 111, Wraith 60.34 with 116, Bunker 60.05 with 119, Ab-Zero 60 with 105 and Fixer 60 with 100.
Jesus, I've forgotten how to do this... Okay, so we have a mean of 0.6575, standard deviation of... 0.475? I think?* And n=511. Then we're comparing that to:
Legacy: =0.7845, S=0.413, n=116, so Z = [0.7845 - 0.6575/Root(0.413^2/116 + 0.475^2/511)] = 2.9045
Tempest: =0.7561, S=0.431, n=123, so Z = [0.7561 - 0.6575/Root(0.431^2/123 + 0.475^2/511)] = 2.2318
Tachyon: =0.7479, S=0.436, n=119, so Z = 2.0020
Young Legacy: =0.7479, S=0.434, n=31, so Z = 1.1198
Visionary: =0.7258, S=0.447, n=124, so Z = 1.5074
Expatriette: =0.6036, S=0.491, n=111, so Z = -1.0543
Wraith: =0.6034, S=0.491, n=116, so Z = -1.0777
Bunker: =0.6005, S=0.497, n=119, so Z = -1.1361
Absolute Zero: =0.6, S=0.492, n=105, so Z = -1.0971
Mr. Fixer: =0.6, S=0.492, n=100, so Z = -1.0748
So, to put those Z-values in perspective: any value above 1.6449 (or below -1.6449) has a less than 5% chance of occurring if everything was perfectly equal. So statistically, Legacy, Tempest and Tachyon may be overpowered (or at least other factors result in them winning more games than the average), but none of the heroes at the bottom are statistically underpowered... The chances of Fixer's figure or worse coming up on a perfectly average hero is 14%.
*My formula for the curious, though it's probably wrong: S^2 = [Sum(x^2) - n(mean^2)]/[n - 1].