I'm afraid I will have to disagree. The system is poor and not fit for purpose. So much so that were I in need of assistance I would not use rail at all, other than those TOCs providing level boarding.
It will never work adequately until:-
1. A specific, named individual takes personal responsibility for the assisted person at every step of the journey.
2. Hand-off must be in person, with the previous named individual and new named individual both present in sight and earshot of the assistance user to "sign out" and introduce themselves respectively.
3. The current named individual must not "abandon" the assisted person, e.g. leave the train to go and drive the next one, until such time as a handover as per (2) has been conducted. Nor may a driver depart from the station where the assisted passenger is to disembark until (2) has been conducted.
4. No situation must be allowed to arise where the assisted person is not in the care of a specific, named individual, between the point of presenting themselves for assistance and the point of leaving the train at the destination and the named individual having confirmed that all lifts etc to exit the station are in working order.
(3) must apply in all circumstances, even (arguably especially) an emergency evacuation.
Yes, it's onerous, but otherwise we fail vulnerable people.
Best get the level boarding sorted, hadn't they?