Which is what you'll get with a third runway and why with the only sensible solution (the Estuary Airport) you'll sleep peacefully whilst planes fly 24 hours a day on the other side of London, like a proper hub airport
(1) with a third rwy, respite remains, although less than with two rwys; with a third and fourth rwy, respite is as it is now.
(2) It's not only about sleepness nights, it's about daytime respite as well.
(3) An estuary airport cannot work if LHR remains open, so in the theoretical event of it being built and LHR closing, there would be plenty of sleepless nights as local people lose their jobs.
(4) An estuary airport cannot work if LHR remains open, so it isn't going to happen. LHR isn't closing.
(5) Of course we need a "proper hub airport" - at LHR, with 4 rwys.
OTOH the taxpayers i.e. us will be on the hook for the (rather high) cost of building this new airport whereas the third runway will mostly be funded privately with the exception of the new rail and changed road links AIUI.
Another reason that it won't happen.
In principle I support the idea of a new four runway airport for London. Regrettably it seems there would be too many financial, commercial and environmental issues with the proposed location and that's without accounting for the massive delay before such a new airport would even be partially open.
Yes, it is completely impractical for the reasons you list, and others. The Airports Commission has buried it, let's do the same.