I think HS work could be considerably improved if there were less stops - I think most diagrams still have less stops than the main line equivalent but it’s still a lot.
As I understand it the classic services were slowed down considerably when high speed was introduced - they used to do Ashford - Tonbridge - Sevenoaks - Waterloo East - Ch+.
Most SE classic mainline services now seem to be all shacks once they get outside the M25.