I don't agree because I feel that customers physically standing waiting are more important than other paperwork that may or may not be for the benefit of other customers.
I disagree. Just because someone is visible doesn't mean they have to serve you
Just because a customer is not physically standing in front of me doesn't make their issue any less important than yours.
In fact if I am having to do follow up work after they have left then their issue is actually more likely to be more important than your issue.
If I can get a customer issue dealt with while they're there then I will, but if it is a bigger issue that is either going to need my undivided focus (aka cant be done in the odd snatches of downtime between serving customers) or requires a lot of form filling/use of the computer but doesn't necessarily require the customer to be physically present I will get their contact details and contact them when it has been dealt with. I then factor that work into my closing/handover and so whilst I am busy dealing with that I am not doing nothing, I am serving my existing customer who was "in line" long before you were.
I think that the bank should ensure that they have appropriate cover in place to enable you to leave within a reasonable finish time but with more than 1 till open.
This is a valid point but something that is out of staff's control. If they have to leave at a set time they have to ensure all of their tasks are done by that time. Sometimes that will involve tasks that are not "serving customers" and they have no choice in the matter. If their shift finishes in 20 minutes and they know that they have 15 mins of admin tasks to complete then of course they are going to prioritise that over customers waiting in line as they can't guarantee that the last customer won't need 30 minutes of help.
It is down to managers to manage their staff and rotas to make sure that they have adequate staffing levels for the situation but they are human and sometimes they get it wrong, or they get a sick call or someone is delayed etc and it throws the plan off.
Maybe on a Tuesday afternoon it's usually quiet so they have minimal staffing after 2pm but that particular Tuesday they have a rush at 1.30pm ... that can't be accounted for and the staff leaving at 2pm can't be forced to stay late.
Or maybe there would normally be 4 cashiers, two leaving early and two staying late ... but on that particular day Sandra phones in sick so when Phil and Linda leave, poor Margaret is left to deal with the crowds alone.