LO,
You raise some important points, so happy to respond - hope this is of some interest.
First, multi-service commonality - not quite the same for the two programmes. V-22, as I'm sure you know, was an Army led programme for all four services, with buys anticipated from the Army, USAF, USN and USMC. The Army bailed out early on, USN fell by the wayside, leaving USMC as largest buyer to run the programme. USAF is still in the programme, by the way, with CV-22. Aircraft much the same for all customers.
If you think the USMC are trying to use the V-22 as a helicopter you are, I am afraid, incorrect. It will be used as a tilt rotor, and a key challenge is getting the users to understand what that means. I'd bet on the USMC working it out. USAF are pressing ahead with SF missions that exploit the platform's performance, and my bet going forward is that these will supplant many of the conventional helicopter SF missions.
JSF was always aimed at being a larger number of partners, but buying three distinct aircraft from one family. Just like Typhoon, a larger buy, especially international, lowers unit cost and also (importantly) makes it more difficult to cancel. Things get 'political'. Air Forces love that last bit. (Does anyone seriously think we'd still be paying for so many Typhoons for the RAF if it hadn't been multi-national?).
Risk and cost - no doubt that V-22 carried lots of risk, but in areas where they really didn't expect it - namely structure weight. The tilt rotor technology hasn't caused them major issues. F-35 has also suffered really serious cost escalation, but it's most visible technical risk was always seen to be the STOVL platform. In fact, it's probably the software that's going to cause most problems now.
Your point about how commonality has compromised F-35 design has some justification, in so far as any aircraft design is a compromise to some extent. Typhoon is really an out and out AD aircraft, and a very good one. But it has sacrificed air to ground capability to get that. F-35 was, from the start, and explicitly, a multi-role aircraft, a 'strike fighter', with exploitation of LO built in. That has driven key features including internal weapons bays, which have a massive effect on layout and structure. The fuselage is not short, it's just really, really broad, under the wing. It's effective wing area is actually very large.
Where the LM team did come unstuck was in not having the right weight estimation tools to cope with an airframe that had large holes and bays in it. On top of that, some of the detailed structural design was, well, uninspired to say the least. Those issues got fixed (as far as they were able) during the weight reduction effort.
It might be useful to remember the US background to JSF. They were looking at the wreckage of no less than four failed combat aircraft programmes. The common features, as seen by the Pentagon, were twin engined designs (grew too big to afford) and single service requirements that generated single role aircraft which were unsaffordable. The push was therefore to go for a single engined design to fill a wide range of roles and accept the compromises that this would involve. They had to take a decision that would take 20 years to work out. I think they deserve some credit for trying.
USMC F-35B CONOPS do envisage forward strips, I think the strip length is 1200 ft. (Could be 1500, not sure). Short landings, short take offs. No vertical work. Logistics at that site are not very demanding, given their concept of ops, which is to launch from the ship and land at a bare strip ready for call forward for CAS by Marine units.
The best answer I could give to your question (where's the scenario?) is to go look up some of the openly published USMC material that's out there. You probably won't agree with it, but as ever, it's your right to disagree. Evalu8ter makes a very good point - the USMC have long memories and are going to fight hard to retain USMC owned air for true CAS missions to support 'the Marine'. They are certainly NOT going to go relying on the Air Force any time soon.
They have solid political support and massive public support. That is why, for some time, I have offered the opinion that the F-35B is highly unlikely to be cancelled.
Best Regards as ever,
Engines