Actually they're split in to much smaller groups. In the eyes of management even Stonehaven and Peterhead are seen as totally different entities. The "Bluebird side" is more profitable so it's common logic that it gets more investment.
That's true of most depots in most regions, but it's not on the same level of separation as formerly being different operating companies and still dealing with the legacy of that.
My comment was not meant as a critisism of where investment is directed, just that you are only commenting on what the "right" hand (Bluebird) is doing....there is a whole other "left" side (Highland) that exists.
It all comes down to profit and reliability, hence why the priority is to replace the unreliable KX58 Panthers at Aberdeen as these operate on the Deeside 201/202 which have came under lots of criticism of late. The B7Rs while in quite poor cosmetic condition still prove cheap to run and fairly reliable (When compared to Panthers).
For the routes Bluebird run the B7Rs on, maybe. However that does not mirror the experience of Highlands or the few other places in group that operate them. The writedown that group seem to be willing to take on B7Rs also suggests that they're out of favour.
I would suggest/speculate that once sufficient vehicles are available to cover the D&E work without relying on Ferrymill and inter-group loans, you'll see the ex-D&E Volvos migrate up to Orkney, while B9Rs backfill at Inverness and replace B7Rs at Aviemore.