So, while I was at it, I thought I also made some graphs of the win percentages that the factions achieve on the different maps in automatch in January and February of 2020.
Disclaimer(s): Deriving anything from automatch statistics is somewhat tricky; the matchmaker is supposed to level out player and faction power levels, while on the other hand being limited to the players that actually queued. It seems fair to assume that the matchmaker is only taking into account a player's performance with a single faction and not the map - which is why I think there is some point in looking at these at all - but previous studies showed that map vetoes do depend on the player level so, there might be some imprint of this.
The values below show the difference between a faction's win percentage on a specific map and its average win percentage. I also computed estimates for the standard deviations with a pretty crude boot-strapping technique. I didn't display them in the graphs to not clutter them further, but I'll add some sentence on the estimated accuracy to each section. Note, that generally the values will be more accurate, the more often that specific faction played on this specific map. Conversely, values for less popular maps with less popular factions might be severely less accurate. I put a gray rectangular on the plots to indicate the part that is roughly reflecting the typical uncertainties.
Note: The maps are ordered based on their popularity. The most recent numbers can be found here
I have no means of checking which side each player started on. In turn this means that maps that have very advantageous starting points (like, "North side will always win!") will end up with very balanced stats.
Finally: Don't fret over the implications. Even the more extreme values below barely exceed a few percent. To put this in perspective: Assuming your faction shows a -2% win percentage on a certain map; this means that out of 100 games you play with this faction on this map, you loose only 2 because of the map; the other 98 games are decided by the players' skill gap and faction balance (so, matchmaking stuff), starting position, random elements and other things. So, practically this will hardly be noticable.
I recorded 155284 1v1 automatch games (yeah, I think my server had some "disc-full" issues for a few days...), about 82k OH, 78k SOV, 73k OKW, 45k USF, 31k UKF. Win percentages are roughly 0.6% for the more played maps and factions but go up to slightly more than 1% for UKF on the lesser played maps:
I have data for about 190k games (AT and RT). I broke the numbers down to team compositions. Most common team was OH/OKW (108k), the least common was UKF/UKF and USF/USF (10k and 14k). For the other compositions I found between 34k to 51k games.
I have about 120k 3v3 games. The diagrams below show the axis win percentages (obviously, allied win percentages will be opposite of those). Uncertainties turned out to be 0.4% for the more commonly played maps to the 0.8% for the less commonly played ones.
I found the data for about 230k 4v4 games. The inaccuracies I found are about 0.3% for the commonly played maps which increases to 0.7% for Vielsalm.