The Inv - Ed A9/M90 etc. experience is grim, but the 170s are worse if you marry-up cost, time, convenience, passenger comfort and general pleasure. Not that the 170s are a actually a bad train, before I get shot down about that. It's just, all things considered, they aren't suitable for the route.
You also have to think that sitting relaxing on a train with some of the best views in the world whizzing by is, in itself, a driver for people to take a train rather than drive.
That's why it's disappointing to hear that the focus of the new HSTs is on lines already pretty well served by LNER, XC and so on. The greatest uplift in experience and capacity will be on the HML, with Aberdeen - Inv a very close second. Sadly, those routes seem to be second last, and last, respectively, in the SR priority list.