They should! Although the 3 off the top of my head (Sun Air of Scandinavia, BA City Flyer and Comair) have all been on a (slow) downward trajectory I feel. I've not flown any of them as much as BA mainline, but can certainly see a few differences as the years pass.

I did JNB-HRE a few years ago in Y, then JNB-WDH last year, and there were some fairly big changes (no spirits, no hot food). Sun Air too I think have cheapened out in the catering of late, although the overall product is still probably the best in Europe.