Yes some people thinks a lawn mower is Bush Hog (larger rotary mower attached to tractor and is designed for rough cutting with swing arm bar blades).
I just recently by accident nearly destroyed my riding mower deck by hitting a large stump. Bent the blade, broke the spindle housing, and bent the deck itself. Kinda good I did as also had head gasket to blow on the engine. A couple hours with a large 3lb hammer I got the deck straighten out. Replaced the whole spindle assembly and new blade. Usually I am fixing others screw-ups but I reckon it was my time.
Yes some of the Briggs OHVs are using light weight flywheels that just can't take the abuse. I haven't seen broken as you describe but I seen them split in two. There was even a picture here of one that riveted back together.
