Both leveling system and on board gensets are available. Many new units now come standard with leveling systems.
My unit came standard with leveling system. I had a 5500 Onan LP factory installed.
Both features work very well.Push button leveling as well as push button electric power.
These features are all about convenience. With them there is no need for: leveling boards, legos or portable gensets,gas cans, parallel cables or any of the other stuff required.
Having A/C at a rest area is as easy as pushing the button. The LP models do use more propane, however they do not suffer from the carburetor issues that plague gas generators. My unit comes standard with 80 # LP which can carry me a day or two if needed. Generally I don't boondock for long periods, but use genset for lunch stops and overnight stops.
In the end I agree with the OP as I have both of the options he wants and I would not have it any other way