This would happen to any airfield anywhere, and is not a specific problem to a Thames airport.
True, if they had everything straight ahead to 5nm before turning. However, LHR SIDs split earlier, so we can get 1 minute departure separations. So we can theoretically get 60 departures airborne in 1 hour from one runway, assuming the same wake category. Therefore, you're getting the same theoretical maximum departure rate off your two runways on a £XXbn man-made island than we currently have from LHR.
And a better explanation for why LHR should be closed down would be harder to find.
And yet you seem to be the only pilot who's complaining!!!!! We've done it that way for years. So have other airports. Where are the reports of airliners flying into the ground due to infringed ILS sensitive areas outside of 2nm from touchdown?
So you'd spend £XXbn for an airport that would not actually deliver
any capacity increase. You're just moving the same amount of traffic to the east of London.