To add my comments
I suspect limited space on the ground meant using height and floors. Personally for me its a damn site better using escalators and lifts rather than walking for miles around those huge terminals encountered in the USA.
Security - not great, but still better than most parts of the world which shows just how bad security generally is
Bussing to planes - Absurd really but given the terminal space governed by height not width - thats a limitation of the boundaries of LHR
As to lounges, not sure why the policy of BA is an issue of the terminal itself.
Overall design - well its there to make money for BAA, not a convenience for the PAX.