I feel like the 'risks' of unattended gate lines are being grossly overstated. By far the biggest risk is being slightly delayed if your ticket doesn't work.
This TfL FOI request from 2023 states a total report of
1 injury in a gateline - and doesn't even state whether it was attended or unattended. I don't remember the number of entry and exits there are per year, but I'm thinking 2-3 billion?
Obviously I think best practice is to provide a staffed gateline, but seems like TfL has decided that there is very, very little risk of injury.