I would disagree, they already took the necessary level of personal responsibility by using an ECV and Disney decided for whatever reasons not to allow the ECVs in the queue, so at that point it would be Disney's responsibility to accommodate a legitimate mobility device in a reasonable manner.There has never been a requirement that CMs push anyone through the lines, ever. There is a degree of personal responsibility here, including ensuring that when accessible entrances are available, the guest takes the necessary steps to avail themselves of the provided accessibility. Just as Disney is not required to provide free wheelchairs, neither are they required to provide someone to push those wheelchairs.
The best is to provide a viable alternate entrance, but failing that if the person has no one to ouch them in a manual chair, but is using an ECV, then a CM pushing them is a reasonable alternative. Again, the person needing assistance did what they needed to do and already took personal responsibility and ECVs are considered mobility devices that must be accommodated.