I think you are being rather naive expecting one controller to only be dedicated to a relatively small bit of airspace. You have to remember that it is also the function of Thames Radar to control the aircraft inbound and outbound from both Biggin Hill and Southend.
Not strictly true, in that the airspace around Biggin Hill ATZ is Class G.
Controller workload seems to be a more common problem, not just in the south.
I have twice recently been told to "stand by" and remain outside Class D for protracted periods. In one case the delay was made worse by the controller allowing other similar VFR traffic, which called up after us and was further away, into the airspace well ahead of us. Having held for ten minutes plus, we assumed ATC had forgotten us and we called again, only to receive a terse reply and told to stand by again.
In cases like Farnborough, we arrive at the situation where GA pilots have Class D airspace control forced on them, sometimes to benefit a small number of users. Then when situations like this occur, pilots are told they should be grateful for the service they have been getting in the past because they aren't paying for it. It's not surprising that folk object to the airspace grab in the first place, especially where it would create one or more potentially dangerous choke points to traffic obliged to to fly around the airspace.