BART is an oddity as accessibility goes - it was pre ADA, but disabled advocacy resulted in elevators being built with the original stations. It was ahead of its time in 1972, and far behind its time in 2022. The $2.4 billion Berryessa extension, opened in 2020, has only one unreliable elevator per station platform. (The parking garages have 4-6 each, though, because god forbid the suburbanites have to wait to get to their Tesla.)
Even the value-engineered GLX stations are better than that. Lechmere has three elevators across two headhouses, Gilman two across two, and Medford/Tufts and Magoun two in a single headhouse. Union and Ball only have one each, but both have a fully accessible non-elevator entrance as well. East Somerville should have an elevator to shorten the path, but it's not the worst ramp I've seen.