If you look at the program from a meta perspective, B was also hoped to feed (and up production runs) the "not quite a carrier" carrier fleets of folks like UK, Italy ... et al, (I'd need to check on Spain, can't recall if they've gone for a similar capability) who have carrier borne aircraft but no catapults.
Engines, I appreciate your technical perspective on that, but will suggest to you that the "If it's Joint it must be better" attitude did indeed originate on Capitol Hill. As previously noted, JPATS/T-6 Texas II is one such goat rope.
Joint Acquisition in selected sectors is actually a good idea. Beans, boots, common comms suites, and more all benefit from economies of scale and reduced duplication.
Enough on my personal peeve, the services adapted to the Political Requirement (Congress writes the cheques) because they had to. A whole lot of kicking and screaming went on internally, not all of it for public dissemination.
