The F-35 variants are all very good aircraft designs. The F-35B cost is mostly due to a more complex and expensive propulsion system ($28M vs $12M for the A & C models). Adding a clutched shaft driven lift fan, swiveling exhaust nozzle, and bleed air roll control system is no small task.
If you consider the F-35B to be a dud, then you must really hate the far less capable Harriers used by the USMC.
Maybe some of you recall how the early models of the F-18 did not meet some requirements for range/payload. Yet it still turned out to be a very good aircraft.