Tbh, alot of capacitor regulated alternators work very well & very reliably. Markon, Meccalte & NSM capacitor alts all work very well.maybe a different AVR set up, i know that warrior welders generator i have claims to have a "modified AVR (Automatic Voltage Regulator) that reacts to an inductive load, delivering a non-fluctuating current; ideal for running a Warrior single-phase machine, particularly the Warrior 250 Single-Phase MIG Welder."
compared to a more basic capacitor based voltage regulator that some of those brushless alternators have maybe that makes all the difference,
I have found that it will run my mig at 200+ amps without breaking a sweat, but stick welding at 115amps does make it sound more like its working! not sure why?
They have to be set up right & not messed with, as a Capacitor Alt gains (& loses) voltage with engine speed/frequency. Stay within the limits and they are fine for most loads.
They do not like inverters though for sure. I've seen a capacitor fail in just a couple of hundred hours driving an inverter. It's only a guess, but I think the high frequency switching going on in the inverter, ages the capacitor.
Mind you inverters & UPS especially are voltage and frequency sensitive AND create Harmonic Distortion - which is also why they don't "get on" with a lot of small engined 2-pole, 3000rpm gennys (even with an AVR)