I've never had the latter problem with mine, but it DOES have the same fixation about using miles of stressful narrow roads to save a couple of minutes. Some of them are only suitable for my van (which it knows the dimensions of) as long as I don't meet a white van coming the other way!
At the other extreme, it will sometimes take us a much longer route just to be able to include a few miles of motorway!
However, I've recently discovered how to direct it to go a certain route, without programming in lots of waypoints or avoidances. So on any long journey now, I take a few minutes to compare the planned route with a map, and if I see long stretches of "white" roads I'll tap a couple of points along the route I want to use. Useful feature.
BtW, welcome to the Forums!