The F4 differed by being used by Air Force, Navy, and Marines. This created problems due to differing operating environments and missions. Because of that a large amount of customization occurred any way. Interchangeability soon began to degrade and retrofitting was required. The big cost savings were an illusion. Some examples were different engines and refueling systems between the Navy and Air Force. Once you change engines and fuel systems you have lost a large amount of interchangeability. The same thing will probably happen with the F35 where demands are made to customize it per service branch so that eventually only the exterior looks of the fighter will be the same but all the internals will differ. You will end up with 3 different aircraft anyway. Three different variants meeting three different requirement sets with three different test and upgrade cycles. You might as well produce three different aircraft.
The F4 was supposed to work with the Navy, Air Force, and Marines. But it worked so poorly requiring so much rework that instead of ordering one aircraft in the 70's for a replacement several came on line filling different needs for the different services. The Swiss Army knife approach was abandoned for close to 30 years.
So what if the A-10 is a one trick pony? If it is what we really need then go with it. It does it well and can survive a hell of a lot of abuse, the infrastructure is in place, and it is proven. Use the right tool for the job.
I find saying that the software is not supposed to work until next year disingenuous. The deadline already slipped. You make it sound as if everything is on track.
Even adjusted for inflation cost over runs are at about 100% Bankrupting the nation will do far more damage to it than an enemy state could.