sleaver
Veteran
It is narrower and you are right about people would need to know it and be honest in my opinion.Whitedown would be a worse bottleneck than Leith as it's even narrower I think.
White Down is probably best described as Leith Hill but without the flatter bits and as mentioned before, it keeps getting steeper.
When I tried it, my legs (well, probably my mind) gave up twice and the other people on road bikes who didn't stop were going slowly. Although I joked with someone on a MTB just casually spinning up it that I needed his gears
By no means is it a difficult hill compared to other parts of the country or if you like climbing, but if someone has to walk Leith Hill, they will be walking White Down.