Defruiter you are correct, there are no CDAs in to LCY which is probably why DFC never gets the opportunity to fly one there.
.4 yes, I did mean what I said. CDAs and 2.5nm separation/spacing are quite compatible 90 plus percent of the time.
When I start TEAMing or otherwise using both runways then CDAs for the most part go out the window for at least some of the time as that's when vertical separation comes much more in to play.
Unfortunately crews in to LHR are so good at and used to doing CDAs that when you want good rates of descent for separation or otherwise want to manage the vertical profile it can be rather difficult to get the message across.