In the days of the National Bus Company, there were some long routes inter-operated by adjacent regional NBC companies, which were far longer than normal bus routes, but operated as ordinary bus routes rather than as longer distance coach routes. The one that always struck me was one run, as I remember it, by Southdown and East Kent, between Brighton and Gravesend, right across Sussex and Kent, which I think took hours. I was in Brighton for some years and always meant to spend a day doing that journey and back, stopping at local bus stops all over the place ... but never got round to it.
That raises the question of whether it was "unnecessarily" long - maybe not many people went end to end, but there would have been very significant chunks of it providing easy direct connections where there wasn't a simple rail alternative. But I have no idea how that compares with the length of present-day bus routes in the south-east (or indeed anywhere that's not wholly rural)?