I would agree with you WF. The only thing is that the Marchetti stuff doesn't look that expensive. Too expensive for small numbers, but something short of Walmart. Marchetti is a premium maker of supplies sold by Strawberry Cycles, who sells stuff to the good and the great in the custom field, if surely not these MIG welders. Walmart does not equally well penetrate a lot of countries so possibly in some place like Italy the wally world level bikes are smaller scale and medium nicer.
I do think some of the chinese stuff is hand MIG welded. Just from the look of the bead. Badly done TIG, really bad, looks like they guy couldn't get it going, there is lots of different sized and spaced stuff. The badly welded frames of a not quite Surly level, look like a good smooth bead that didn't penetrate well enough, kinda like someone put a necklace of string around the tube. That tends to be the last thing that comes together with TIG. If you have it together to make effortlessly nicely spaced dimes, then it should be possible to get the setting and pace right for the right penetration. Meanwhile the typical MIG weld, looks casually as if it was expertly done, but the penetration is likely wrong. Anyway, there is a lot of welding, with a lot of machines, and I have only seen some of it, mileage may vary.