I don't think it's the fact the motor is small or facing forward.
Imo. It's the fragile gearbox with the intermediate gears on a shaft through bushings in the center of the chassis.
I owned one of the legacy k4s and happened to catch excessive wear on the intermediate shaft to the point bronze filings could be seen. The brunt of the load on the axle gear is taken on one side of this shaft.
Remove the bottom cover on the Legacy H10 and you will see this gearbox setup. My k4 had maybe a couple hrs runtime at most. Whether it was a burr on the shaft, defective bushing, or simply the fragile design. I suspect more of these failures will be occurring over time.
It's not simple, robust setup, like a worm running over a nice wide axle gear.
This gearbox style is also used in the heavy and light mikes, as well as rear facing motored Legacy mohawk, Legacy m1A, and first run Legacy class j. There may be others.
All one has to do is peek between the spokes above the driven axle to see if the intermediate shaft and bushings are in the chassis.
Check out the :20 mark on this video ( not mine) and you will see the shaft in the bushings above the third axle:
