Makes sense, you’re need more capacity up front for your application.
And can’t go hog wild in back due to jack clearance and you really don’t want to widen your rear stance on a dually for off the beaten path, possibly tighter conditions.
Agree, 20s might be the best of both worlds. If you’re already going to invest a significant amount into aftermarket wheels, maybe consider removing the front dually adapter and running a matching conventional rim up front like a srw truck. Then you could effectively maximize the tread width/tire capacity up front and run skinnier but same diameter tires in the back.
Sorry, this is off topic from the 19.5s.