If we look at the gear contact points, we can say that the spur&pinion contact point is good or not much can be done there in reducing the size of the contact point, but the next contact point between the spur and idler gear is much larger and the contact tip of the idler can be reduced to a good size(3mm to 4mm) . In addition, the contact point between the idler and the diff gear is even larger(12+mm) when only about 4mm is needed... My m03 manta ray diff is around the 5-7mm mark which I thought was huge for such low power, but tamiya seems to want to continue down the chunky gears path(maybe for perceived durability) that keeps hurting performance...
I don't even want to mention rotational mass losses, windage losses, noise losses, and gear vibration(wiggle) losses....