I drove 89 throug Neihart some 20 years ago. I thought it was a nice scenic interval in an otherwise flat and open route. But I was in a SUV, so can't say whether it's too steep/curvy for an RV. Google maps has tools to explore that yourself - zoom, streetview, even the bike routing gradients.
Routing progams don't choose by easiest - unless you have some sort of rv/truck option. Usually the choice is based on time - distance and estimated speed. Sometimes a mountainous route may have a slower estimated speed, but I think that's more based on road type than some sort curve or gradient measure. The route through via 89 is both longer and shorter.
Atleast on a full computer interface it's easy to explore alternative routes - just drag a point.
(The gradient option for bikes isn't much help here; it recommends something totally different, using a lots of local roads rather than the main highways.)
Kings Hill Scenic Byway
