That’s the theory. In practice, the length of time journeys take as a result of not having step free access to tubes can be a major obstacle to making that journey. If the combined bus routes take 2 hours where the tube takes 40 minutes, it places a very real practical limitation on your choices.
Having been on the Tower Hamlets accessible transport forum before we moved out of London, TfL aren’t attempting to make all stations accessible over time. Just to try to identify the most viable in a given area so you can get within range of where you need to go and either wheel, bus or cab it to your destination once you leave that lone beacon of accessibility.
Maybe they will very slowly spread step free access once that initial goal has been reached, but the Victorian infrastructure does present some issues, as you’ve said.
What’s hugely frustrating is the lack of joined up thinking. When they closed the Whitechapel Art Gallery exit at Aldgate East for months to make upgrades, for example, they had an opportunity they could have used to build in the step free access then, which would have been incredibly helpful, given the lack of general accessibility for tubes in that area. Aldgate, Aldgate East, Liverpool Street, Tower Hill, Old Street and Whitechapel were none of them properly accessible, even if the odd platform was step-free to access. But it wasn’t part of the overall access plan so they didn’t bother. The token step-free station in the area now is Whitechapel with its Elizabeth Line access, years later, but they could have made Aldgate East step free then without further inconvenience while that exit was closed.
Much as I would love for all tube stations to become accessible in time, it’s simply not going to happen.