Are you seriously suggesting no lines at all should ever be electrified?
There were express DMUs based on loco hauled carriages (6 car transpennine DMUs and the Class 126 that worked in scotland) but they were all withdrawn by the 1980s. They did not last as long as the DMUs intended for local services.
I didn't say no lines at all should ever be electrified, but that it rarely shows a good financial return, takes time and causes disruption.
In the context of the modernisation plan it was largely a waste of money. The business was statutorily required to break even financially. It needed projects that would give a quick and positive financial return.
Just compare the WCML and ECML-it took the best part of 10 years to electrify from London to Manchester with lots of disruption and a poor service for passengers. Meanwhile the ECML services were dieselised and accelerated in half the time at a fraction of the cost and with negligible passenger disruption.
There were certainly DMU's based on loco hauled carriages but I wouldn't describe them as "Express" as they only had a 70mph top speed. I don't think the respective withdrawal dates have much relevance to the type of DMU that should have been built. My recollection is that the Albion engines had been troublesome and after 25 years or so service were replaced by something better. The other DMU's were also clapped out and unappealing to passengers and should also have been withdrawn.