Some parts of roads, like the one you suggest, have naturally imposed speed limits, being the maximum speed it is possible to navigate the corner. As I say, larger vehicles are unlikely to occur exceed 20 due to the angle of the corner.
Speed is not a killer, the vehicle is, and the manner in which it is driven. Speed and stupidity are not the same thing. Sadly the latter is the the largest contributor to accidents.
While other countries raise and lower speed limits at what seems like 100 metre segments at a time, this is both costly and impractical. Of course lives matter. Given the footfall on that piece of road vs accidents, I would say it’s a pretty safe spot. Except for when idiots refuse to wait for the lights to change, or commuters play chicken 20ft from the crossing.
TfL do actually have a few sections of their RR which is 20mph, New Cross for one, but I get the impression that it is not an ideal at all.
While I despise the borough wide roll out of this limit, I can appreciate it is needed in some spots. The danger now is those too impatient to drive at that speed, recklessly over taking.
If any reconsideration is to be had, I would say it was to UP the speed limit back to 30 on certain roads, such as Brockley Rise through to Lewisham Way for example. Sadly I don’t think their assessment and adapt phase has this in mind for a second.