The way I look at it is that there are millions of minibikes that came with very serviceable rear wheel assemblies. The hubs don't just break, the rims are good forever if not crashed or rusted through, 3/4" axle is as big in diameter as a lot of motorcycles and the bearings are a good compromise between cost and longevity, the sprockets are generally not hardened but adequate in as much as they are always of large diameter. What I have seen too often is a miss-match of hub-sprocket adapter-sprocket. Sprocket run-out seems to be a constant problem, but that was never a problem with the 'cheap' stock stuff when they left the factory. Nor, as far as I have experienced, is it a problem with the stuff currently commonly available.