I've tried reworking the thing myself. I think part of the problem is that they moved away from the Beck diagram in 1964, which I reckon was somewhat clearer than the real one. The Met was longer and split further from the Uxbridge branch, the Piccadilly had a right-angle at Covent Garden, again clearer, the Northern was a rectangle, with forks rather than priority junctions at Kennington and Camden Town, and the Circle had a hump at King's Cross-St Pancras, enabling the Victoria to be a straight line, much clearer. I once tried to evolve it somewhat, and got as far as 2001, by which time it included the Docklands and North London. I'd like to show it here, but am not sure about the copyright issue.