The ride was originally designed to start near Doncaster. In 2001 and 2005 We rode from Thorne to the base of the Howardian hills, building up a time cushion before Yad Moss, then the Eskdalemuir/Innerleithen Edinburgh rollercoaster.
The Southern section really started at Thurlby, as the section from the bottom of the Howardian Hills was as flat as a pancake. South of Thurlby, the ride was either intricate lanes or drove roads. From the Southern start, the Thurlby to Castle Howard sections would have dragged, but they were broken up from the Northern start.
There has always been a vocal group which wants the ride to be 'more interesting'. So first the Yorkshire, then the Lincolnshire Wolds have been included. There's a less vocal group which liked the flat section between South Lincolnshire and Castle Howard. They have a 'work around' which involves riding on 'A' roads where possible.
Another outspoken group, which characterises deviation from the published route as 'cheating', ensures that the flat alternatives are not widely advertised. The current dominance of GPS ensures that those without maps follow the route, unless they fall in with those in the know.
I've ridden the Devil's Beeftub route on a 600, and it's easier than the Langholm/Edinburgh rollercoaster, as it's one big climb, followed by a continuous descent.
So the hardest LELs were probably the 2001 and 2005 London starts in Essex and Hertfordshire, ignoring the weather.