Silverstrata
LGW have a 'follow the greens to the stand' system. Its a doddle.
It's only a doddle if the lighting panel operator can actually see the taxiways. If they can't due to fog, then Low Vis procedures become operational, and thus the flow rate decreases.
Heathrow (like HD commented above) also has the follow greens. If it's such a doddle, how come Heathrow and Gatwick have reduced flow rates in fog? Aircraft can land CAT III and they can follow the greens! By your logic and argument there should be no difference to CAVOK.
If, like you say you are, a B767 pilot, I would suggest you get someone in the know at your airline to contact NATS and arrange a visit to the control tower. You might learn a thing or two how ATC actually works.