Many cars try to turn right from Devonshire Rd onto the south circ and this is tricky in the rush hours. If this was made a left only turning then I feel that would unclog this road. (perhaps an exception made for those theoretical oversized lorries that are lost.)
I can't remember back to before the no entry on MM, when David's Rd was reported to be clogged up with traffic, but again it might have been caused by traffic struggling to turn right onto the South Circ. Again make it a left turn only.
When tfl finally install that one-stage pedestrian crossing we have been promised, there would be plenty of time for any potential David's Rd tail back to clear.