i can't help but feel that Unions have been rendered pretty impotent
Not at all. If the CWU announced an indefinite strike until the future of Royal Mail as a service instead of a business, had been secured, how long do you think it would take to resolve the dispute – 3 days ? 4 days ?
As long as the CWU ponces about with ineffective one day strikes, multimillionaires Alan Crozier and Peter Mandelson will sleep soundly in their beds at night, happy and secure in the knowledge that the unelected shitesters can do whatever they damn well want with the Royal Mail.
Wake them up in the middle of the night to inform them that the CWU won't be returning to work until there is a satisfactory solution, and they will be frantically phoning government ministers in their pyjamas.
Of course if they had believed that there was a real risk of real industrial action from the start, then it would never have got to this in the first place. So the CWU's non-militant past, is part of the problem.