I want to hone in on this specific aspect. (Not that it distracts from the rest of your otherwise salient points)
This is where Ravenloft "nightmare logic" comes into play. The Mists can distort things so that natural talents fail. A druid or ranger might know how to navigate a forest well (hell, it might be THEIR Forest!) but when the Mists get involved, reality distorts. Trees move, markings disappear, trails bend in on themselves. Why? Because the Mists are testing them. Or the presence of a powerful evil entity warps the area around it. Or maybe there is no why. And that is what is frightening, the idea that your otherwise infallible talent has just failed and you don't know why except the woods have gone strange and there is a crying girl somewhere in the distance...
Yeah, it's a cop out to have the Mists foil the PCs abilities, but as discussed before, D&D as a system was always too consistent to invoke fear without some neutering.