Prophead
There speaks the voice of someone living in the home counties...
Actually there speaks the voice of someone who has lived most of their life within view of LBA and used to use the LHR shuttle weekly.
Your post could just has easily have been written in support of a third runway. People keep arguing against LHR expansion based on the fact that the current arrangement doesn't work. They know that and this is why they want to expand. Domestic routes do get cancelled due to over capacity which is precisely why a third runway and new terminal with good connections is needed.
In regards to being put on buses, this has happened far more to me when travelling by train that by air. This is however the reason why I believe people would rather be stuck in London than Amsterdam.
I really don't see LHR as a London centric project. The amount of connections and access this could provide to the regionals means it's a win win for the whole of the UK. Those people you mention using AMS etc. to connect are all spending money that could & should be being spent at Heathrow.