My Experience is yes, they are inferior, mostly in chassis, shocks, etc.. however I bought my son one when he was in that in between stage to small for a larger bike, to big for a 50 etc..It was a 90 cc.. I knew he only needed it for about 9 months then he could have enough height to jump to something bigger. We ran that thing into the ground, all of us adults did as well,, it did everything my other sons xr80 did, just with a little less finesse..The engine was bullet proof, It was wrung out to within an inch of its life many times as he struggled to keep up with us on bigger bikes. Engine and transmission never so much as hiccupped, the shocks were springy, and the rear brake pedal was flimsy, but it never failed to start and run, and run perfectly for the year we had it and abused it. I recall I paid something like 490 bucks for the thing, had to put it together myself. it was a VERY good bargain!
So you go into knowing there may be a little more maintenance, a little less performance, etc.. but then again, you usually pay less than 1/2 that of a Japanese rival, and you have to weigh that in the mix. I would have zero issue owning one as a commuter bike, occasional dirt road/ trail bike.. etc.