I started tracking my games at the start of season 4 to see if I could find patterns to improve my play. However, it also provides the ability to track win rates based on which classes are in the game. You can find that spreadsheet here.

Theoretically, town should maintain a 60-65% win rate, depending on whether you count NE as a general evil role or its own independent entity. Though town does have an overall win rate of 65.1% over the games I played in, having a Retri in the game improves town's win rate by 50%. The polarization of the class is simply unhealthy for the game, and I argue it needs to be addressed.

Edit: Added to the spreadsheet is some info about town's win rates based on which NK is in the game. Town is 26-8-1 (74.3%) with an Arso, 13-10 (56.5%) with a Werewolf, and 14-11 (56%) with an SK in the game. That means town's win rates improved by almost 33% with an Arso as NK compared to WW or SK.

Edit 2: Surprisingly, town's win rate fell 15% when they had a mayor in the game, from 66.7% to 56.7%.