There is nothing wrong with free wire, nothing wrong with a neutral but one doesn't need to go out of the way or add expense to put it in either. You will not overheat an 8 with anything that has factory cord and only 250 migs require that and then only at top end not found at home anyway.
Nothing wrong with 6 wire either, its only 2 sizes bigger and in some cases 3 that actually needed to serve the load. About like an inch pipe to supply a 3/8 air ratchet.
In the case of welders and other equipment it is meant to be plugged in to a current limited circuit possibly without other over current protection. The mfg supplies it with a cord and wire sufficient and an end on it to match opcd.
The internals of the machine are designed for this, in the case of the welder it has a fan and wire safe to hook this machine to a 50A circuit,,,, then a genius says,,, I am special and I will cobble a fan on this "220" circuit. The question is,,, was this fan and now its wire and connections designed for 50A? Was there additional fuse installed for this or other "110" recepts or equipment?
Did the mechanic introduce one, maybe even several code violations or negate safety equipment or even set up booby traps from a modification he made that work absolutely fine without realizing it?
This is an absolute foreign concept to a lot of people. I know people absolutely believe cause something is safe because it works,,, or will go down the road. I know a farm mechanic believes ths in regards to this very issue and cant tell him.