Sure, it has a 51% overall win rate on the NA server, but that hardly makes a tank close to being overpowered, especially considering that it is one of the most played tanks by skilled players. Obviously, having enough unicums playing a tank artificially inflates its win rate.
But for the vehicle’s statistics, it just bleeds HP at every moment, and its gun has horrible dispersion, even with vertical stabilizers, basically negating the benefits of its autoreloader. This is compounded by the fact that it is pretty close to a traditional medium. The Bourrasque can make up for those same weaknesses with even greater speed and concealment, making it much harder to find and hit, hence its overpowered state.