Lifts are of course perfectly acceptable for the diagonally challenged (wheelchairs, prams, whatnot).
Or just get rid of escalators entirely.
Many of the stations are very deep - the equivalent of a 15 storey building. Changing to stairs would certainly lower throughput because that's a really long climb.
I find that incredibly hard to believe. Assuming 4 meters per storey, you are saying that the London underground stations are at a depth of 60 meters.
If true, that's really amazing.
[1]: https://en.wikipedia.org/wiki/London_Underground_infrastruct...