MapQuest is talking to people in cars - not RVs. You're a fellow flatlander. Get a copy of 'Mountain Directory West' and make your own decisions. The bighorns are beautiful. I've driven over them on 16. Going up is slow. Going down the other side there are several marked places to pull over to check your brakes, because you're about to deal with a very long downhill and if you ride your brakes you won't have any near the bottom. And 16 is the easiest of the three (16, 14 and 14a). The signs actually say to pull over for a brake check.
And the Bighorns haven't shrunk any in the last 30 years.
BTW, I've made the trip to Yellowstone several times. I go around on I-90.