I am guilty of running a bin extension. It adds approximately 1200 lbs of extra grain weight.
A reasonable guess would be an additional 500 lbs to each final drive.
If that 500 lbs is enough weight to cause damage, maybe I should ask potential riders (factory installed buddy seat) how much they weigh first.
I guess the point I am trying to make is, there must have been "zero overkill" designed into the final drives. That just seems chinese to me.