My non-expert view is we are only buying capability simply to remain "compatible" with the USAF and NATO and other users of the F-35 with the networked battlefield concept. That is about the only good thing of this aircraft seeing as we are not getting STOVL and will have crippled stealth. The platform itself has low range for our needs, low weapons loads, the single engine aspect as above, it's expensive, not on time and most likely will be outperformed by current 4th gen aircraft.
On top of that any credible threat will be going the cheap and plentiful route (quantity has a quality of its own). I read of some pacific war simulation that focused on logistics, and showed the US would run out of AA missiles faster then they could realistically down Chinese aircraft, and then would still be vastly outnumbered. How much money do you throw after a better aircraft when dozens of good enough will prevail anyway?
The Rhinos for the most part at least keep us in step with other forces and at a price that is far more in line with our realistic needs. IMHO we need a core multirole force like the Rhinos, but we can augment it far more efficiently with cheap semi-disposable unmanned capability, especially with our coastline and distances. I really don't see what the F-35s give us other than maintaining our girl by the phone relationship with the US.