Well folks, I partially agree with you....and partially don't. An inductive load will certainly benefit from a larger generator head. Specifically "in the start". As in "locked rotor amperage". I oversize my 12/1 with a 20 kw ST head, where I originally had a 12 kw ST head (still oversized for the engine, I know, I know). The results were immediate. I was better able to start an inductive load, and keep the voltage vs current phases closer together (thus power). I could witness it on the oscilloscope.
Once the inductive load is up to speed, the current requirements totally change. Infeed power loads on a "starting" inductive motor are MUCH larger than the "run" requirements. And if you oversize your generator head, GIVEN the mass of the flywheels (approximately 50 instantaneous horsepower, by two each, 150 pound flywheels turning at about 1000 rpm, IIRC), you DO gain benefit. I've proved it.
Now, please notice that I never said you could constantly tax your 6/1 or my 12/1 at a constant demand as dictated by that 15kw head. Obviously, that would never work. Should you attempt, you'd find that your engine would lug down pretty quickly, and suffer the consequences of low frequency.