I have driven the the route you described from Holbrook, 377/277/260,to Payson continuing on 87 to Mesa many times towing my travel trailer with absolutely no issues or problems. I have also seen many motor homes on this road and have never seen one in distress on the side of the road. IMHO, overheated brakes are more a function of the driver than the grade. If one does not know how to descend a grade there will be problems no matter how slight the grade is. I have ascended and descended 9% grades with ease because I sought the knowledge to do so and applied it. It is not difficult it just takes some education. People from flatter areas have a totally different view of grades than do us westerners. Anything 7% or less is not all that unusual here, and, while they must be taken seriously, in most cases they can't be avoided and must be dealt with. Glad you enjoyed our scenery and hope you come back for the great fishing and hunting.
60 from Payson to the Salt River turn-off was closed for ~2 weeks a month ago for the fire whose damage you saw. It was a terrible time for all of us here in the Valley and going north. I haven't seen it myself yet but will in about week.
My favorite sign on that route has always been one similar to the old Barbasol signs:
They saw an Elk
Oh what a thrill
Until it landed
on their grill
Slow down and watch for wildlife.
RichH
2017 Ram 1500 EcoDiesel
8 Speed Transmission
2010 Dutchmen 24 FB-SL
Curt 10,000# WDH
Never underestimate the power of stupid people in large groups.