I have neveer heard what you were told before, and i wouldn't believe it without seeing proof on some testing equipment or from lab tests that have been published

My coleman Blackmax (13hp 6500w continuous - 8450 peak actually the RMS rating i was surprised to learn) has about 25 - 30 hours on it and still powers my dynasty 200dx all the way to the max amp output without even sounding too different than running a grinder off of it. I've run some real long beads on genny power. Even using high frequencies in the 160 - 200hz at 200 Amps the coleman held it's ground. The very last time i used it I was TIG'ing aluminum and burned some stick at high amps (Cut/Blasting Rod, 7018, 6013, & 6011) just to see what it would do and it ran as goos as it did the day i got it and the generator never even flinched.