Agree, I once had a trip door to door between Berlin Prenzlauer Berg and Haidhausen (Munich‘s Prenzlauer Berg...) in 3 hours and 10 minutes. Everything worked beautifully and by chance I hopped between different modes of public transport in no time... Compare that to a trip from London‘s city center via Heathrow. In 3 hours you might just have worked your way to entering the plane.
If you're worried about security lines why not fly out of London City? Yeah it's all the way out on the east end, and yeah DLR is pretty gross, but getting from the train to the gate takes about 10 minutes.
