YS, ND and WM are identical to STW stats, and tests show that the performance of these units, except for the turning speed, is the same in SW and STW. The YS is different in STW/MI only in that it has one additional point of armor, but this wouldn't affect melee performance. The perceived difference in performance in SW might be due to bonuses or penalties from the vices and virtues which wasn't a feature of STW or STW/MI.