Comment by jandrewrogers

The F-35 was designed to be a partially-nerfed export version of some of the capabilities in the F-22. It was anticipated that the large production rate would significantly reduce the unit costs, which seems to have panned out. They probably shouldn't have tried to produce three significantly different variations of the same design, since that added materially to the development cost.

The 6th gen platforms appear to be coming in at significantly reduced cost relatively to what they are replacing, which was a major objective.