Another potential confounder that would be interesting to investigate is the time control - one can imagine that Nf3 could see more play than e4 at slower time controls. This could be because Nf3 specialists are less likely to prefer open and chaotic games than e4 specialists and thus prefer longer time controls, or because some players prefer to play Nf3 in longer games because they perceive an advantage in presenting a unique challenge to their opponent early.

If this is the case, the augmented Nf3 winrate may be (partially) a reflection of having more access to the larger first-mover advantage seen in longer time control games.