Yes, you're right, just looked at OpenCycleMap - Smalldean is only on the Chilterns Cycleway, which is well known round these parts for having been drawn up by a masochist, as it seems to hit pretty much every climb or muddy barely passable single track road it can!
Having said that, NCN 57 is equally as perplexing in parts now that I've looked at it - takes you up Kop Hill (possibly one of the harder climbs in the Chilterns) and the Wall out of Great Missenden (25%+ on a single width path), but at the same time uses the flat easy Phoenix Trail, probably making most people think the rest of the route is going to be equally as easy and straightforward!