Why do you have a need to carry around a 6000 watt generator capable of a 220VAC output?
Clearly, you don't really need it, but here is why we are getting it...
It is a 120v generator, not 220v. Onan discontinued the 3200 watt diesel generator that was being used by GXV. GXV could also install a Fischer Panda 7000 watt at higher cost but it would require a roof mounted radiator and there are not many sevice locations available in the US. Smaller diesel generators include the Fischer Panda DC output model and the one designed for Sprinters (higher price, I believe, than the 6000 watt Onan), GXV uses these on some of the other models.
Is 6000 watts overkill, yes, but with the Onan you get a reliable, reasonably priced, widely used generator which can be serviced easily versus the smaller capacity diesels that are available.
The Mastervolt 4000 watt inverter has a 200 amp battery charger to top off the lithium battery bank quickly using the Onan when needed to supplement the 800 watts of solar. This would work fine off of a 3000 watt generator.
The other high load devices are the air conditioner, induction cooktop, and microwave/convection oven. Not absolutely needed but you have the option of running several of these at once with the Onan if you don't want to drain the batteries very much.
Could we easily live with a less powerful electrical system, sure. We had no trouble living in our Sprinter camper van on a 6 month trip to Alaska with 220 AH of AGM, a 750 watt inverter, and a 2500 watt propane generator. Even that would be considered overkill by many.
The vehicle we are getting is our once in a lifetime extravagant purchase, we are retired and are selling our house and will travel full time. No way to justify the purchase other than label it is as a late life crisis purchase, we had no midlife crisis purchases. I doubt we will regret the choice. In the end, it is not that much more expensive than the large diesel motorhomes we originally were looking at for full time travel when we retired 10 years ago. We both had health issues that delayed things and in the mean time realized the more typical travel in a large motorhome was not really our cup of tea.