Glider
Captain
From what I have seen (and I don't pretend to have spent a huge amount of time on this). The first two batches were designed to their length to save costs. Now if you can say that this is a cut in the length, or they were built as designed, albeit to an incorrect length, is probably open to debate.
My guess is that in the design team there would have been people who knew that the design was too constricted and would have lobbied for a better outcome. Ship designers are highly trained, experienced and not the type of people who would have calmly taken instructions without making themselves heard. However they were overruled.
No one seems to deny that they needed lengthening and that the third batch was by some margin a better all round design.
An aside but I joined the RN in 1973 and everyone was very excited as there was a lot going on at the time. A number of new designs were coming on stream, Type 42, Type 82 Type 21, new Helicopters Sea King, Lynx, the possibility of the Harrier and new missiles notably the Sea Dart and the Seawolf.
We had a lecture from someone who was on the Type 42 design team and he explained some of the early thoughts about the design of the Type 42. It was a long time ago and I wish I could remember more of it, but the only thing that sticks was that when they were first bouncing ideas around someone thought about putting the ships exhausts the stern and not have a funnel. The idea being that it would give a smoother airflow over the ship and improve helicopter handling. Obviously this lasted about ten minutes and probably never made it to paper, but it was mentioned as an example showing that no idea was too silly.