I feel your pain about LHR I hate the place with a passion.
Sadly I need LHR as it is convenient but I find my stress levels increases especially when arriving home. Service is awful, the expense eye watering and the stench from the toilets in the main passengers areas appalling.
Like you I find that on very short hops the delays getting air born are scandalous.
I now build in extra time for every journey at considerable additional expense in time and money as well as finding ways to ensure I can entertain myself via games and music while waiting…..generally on board.
It really needs to be bulldozed and a new airport with high speed rail links built……and it can be done in around 5-7 years if there is a will to do so.