The difference between the 'low density' & 'high density' ex GWR coaches isn't that great - 80 seats v 84 seats. 4 tables per coach instead of 2. Not ideal (personally, I prefer an airline seat anyway, but I totally get why some people would rather have a table, for work, laptops, etc). The luggage space is truly pathetic on a 170 as well (even one that isn't particularly busy).
The point is: it's only temporary & the proper Scotrail 'refurb' coaches have a more appropriate layout.
As someone who has worked as a Conductor on the HML, there is most definetly a capacity issue during the summer & whilst sone of the evening trains aren't as busy, the afternoon trains North of Perth can be very busy. The 1253 & 1447 from Inverness also tend to be pretty well loaded too & a 4 coach HST is definetly a welcome capacity increase on those trains.