I haven't kept up on the F-35 lately. But this is a jet made of compromises. The Pentagon knew they couldn't get funding for multiple new jets. The F-35 is trying to do to much by being a jet for the Air Force, Navy and Marines. So they combined all the requirements for the specification. Combining the requirements of the Air Force and Navy probably isn't so bad. The Marines requirement of the F-35 being VTOL capable is holding the design back. I accept that VTOL is a key requirement for the Marines, but the F-35 has made a lot of trade offs for that feature. While I don't know how successful the F-35 would be without VTOL, it has to be better then what is being delivered.