JF is right, of course...
The Marines could do their classic air mission perfectly well with a subsonic direct-lift STOVL. It's not the best for air superiority, but could certainly be equipped to take on a low-level threat (eg Naughtystan with a couple of squadrons of rusty MiGs). The high-level capability of the JSF-B, in the USMC, is in any case fatally compromised by the lack of organic AEW&C.
Supersonic STOVL is fundamentally difficult because of the complexity of avoiding HGI. Adding stealth to that equation makes things worse. Granted that the F-35B can be made to meet spec, it will be expensive to support and have very limited room to add any other capability, both because of volume and VL thrust considerations.
And how did we get into this mess? Because the experts (particularly in industry) assured us that it could be done in the first place, relatively cheaply and quickly. And after the X-plane stage, they assured us again that the risk had been reduced as never before.