We in the US have what you guys are referring as bar blade as long as I can remember.(currently approaching 58). These mowers are only meant to cut properly maintain lawns; not for cutting stumps, tree roots, garden hoses, chains, kid toys and the like. Now do use swing arm rotary mowers but they primary use fields and roadsides. We refer to them as Bushhogs, and many of them have stump jumper discs.
Yes I do see bent blades and bent crankshafts on walk behinds as said they are not meant to be abused. As for our JD riders here most fairly well built other than those dang plastic hoods. The problem now is they have come out with consumer grade machines that are well in my opinion just that and they just don't hold as well. Main here see the public demand for a cheaper product so JD had to reduce cost somewhere.
I do see my fair share of bent blades on the riders too. Most are from hitting tree roots. So far in the last 7 years I have only seen 2 or 3 bent spindle shafts but have more with stripped star blade mounts where the user had either failed to put the blades properly on the stars or simply under torqued the retaining bolts. Now the old Murray Ohio riding mowers did use a 5/8" spindle shafts that were prone to bending but the 3/4" shafts seems to hold up much better.
As for a 2 stroke having more power it makes sense as they producing power on every rev when compared to a 4 stroke that coasts through every other rev depending the flywheel effect.
