Let me put it another way: The F-35A is land-based CTOL, the F-35B is STOVL and the F-35C is carrier-based CTOL, but they're all based on the same airframe. To what extent is each type compromised in it's role by the need to build the other types from the same basic airframe, and to what extent are the capabilities of the whole programme compromised by the need to repalce so many different types?
In other words, would the F-35 be a better F-16/F-18 replacement if it wasn't also trying to be an AV-8B replacement and an A-10 replacement all in the same basic airframe, and vice-versa?
So a quick answer on the political side of things, we saw the ATF/F-22 which is almost the opposite of the JSF-- single service, single mission, single nation, "no compromises" (lol but play along) and we saw a long development cycle, delays, and hge cost increases, and having it curtailed with the GWoT raging, and charges that is had no value in such wars. I think the War on Terror underscores the difficulty in getting conventional weapons fielded as well. THe F-22 was curtailed, The Marines EFV was canceled and of the complaints was because it wouldn't be good in the WAr on Terror (keeping in mind it was never built to fight such wars), and we have seen the army struggle massively with replacing its scout helicopters, and field other conventional systems that replace older stuff.
I think if the various programs had not been rolled into 1 with JSF, all of the F-16, F-18, and AV-8 replacement programs would have been cut, or canceled and the funds "freed up" by doing that pumped into keeping the already fielded and fighting war on terror systems going (which we saw the Army do for example). Which is great and all, but considering it takes about a minimum of 10 years to develop a new airplane (and 20 is far more realistic) and it won't be IEDs and RPGs forever, I think everyone would be scrambling to replace the worn out teen series fighters and finding there was simply no money to do so, thus the can gets continually kicked down the road, and the War on terror doesn't seem to have an end in sight right now.
Joint programs are much harder to cancel, and have the benefit of combining funds from multiple sources. I think big picture its a blessing the JSF program is going to go through delays and all, because the alternative IMHO was basically NOTHING, thanks to the obsession with Iraqistans into perpetuity. So I think if if there are compromises, frankly it beats nothing. Which was a very realistic possibility. So even with hindsight, I would still say it was the proper choice. With hindsight we would try to avoid some of the pitfalls that happened, but the overall idea I feel is still a good one.
I understand that in a perfect world a service would say "we need this, and this exactly" and industry would design it and congress would gladly support it, and not dare cancel it but it really doesn't work that way. You have to get the politics right as they. It was the 1990s cuts and cancellations were happening left right and center the USAF didn't really have the money for an F-16 replacement and the USMC didn't have the money for a harrier replacement. and then in 2001 the game changed. I think you would have 5 programs with 3 coming to fruition (2 canceled programs at least) and that is being highly optimistic in terms of an ASTOVL actually happening for example. The USAF would be trying to justify why it was replacing the F-16 with a stealthy multi role instead of an A-10 for example. the less enthusiastic example has multiple programs with none or maybe 1 or 2 coming to fruition.