KenV makes the point that certain older projects were curtailed/abandoned at prototype phase, for good reasons at the time.
The trouble with the F35 as I see it in this area is that as it is so complex that to be frank a fully functioning initial capability aircraft has yet to be built and or tested thus making an informed decision on the performance of the aircraft as specified not yet possible.
As yet, to my knowledge, no non test aircraft has flown with external stores, the software is not fully functional, i.e 3F is still in testing, the logistics / support system ALIS does not work as it should, making taking a view on maintenance costs difficult and there is also a requirement to respecify the alloys to be used in some structural components at least on the B.
Back in the day, when the broke UK could afford to develop 3 V bombers etc, the time from commissioning to prototype flight was so much shorter than it is today. Aircraft selection decisions are now far more complex and with far greater ramifications than in earlier times.
Let us hope that the F35 can be made to deliver on the promises that the some $50 billion development part of the project has / will deliver.