Sorry - I am confused. The operator did not exist until privatisation - i.e. after the mid-1990s.
You are, of course, correct.
My mind wandered to the beginning of the end of a quality operation on the Brighton Line which, in my opinion, began at the time of the 1978 timetable change. (You may remember the shambles which attended the attempt to interwork Victoria - Coastway West, Brighton and Coastway East services. Curtains disappeared from second class carriages about the same time and now each year seems to plumb new depths!)
To be fair British Rail oversaw the early stages of the decline, the current operator has simply, but effectively, continued the decline. The esteem belonged to the 'good old days' and to the Brighton Line itself. Nowadays any fool organisation can bid to wreck the remains (no buffet trolley, strip out any vestige of comfort in the seating, con tourists onto the GA trains, withhold usable timetable information, the list goes on and I've yet to use the word 'guard').
I used to enjoy a trip up to town; now I never use Southern for the journey. The much derided Southeastern seems now to be in better hands (at least on the mainlines).