I think they choreograph their choice of modules more than people think and more than they let on, particularly propeller driven aircraft and helos, which incorporate very similar technologies, there is little turnaround time, no radar or minimal avionics. I think they push out what they can the fastest, "lazy development". If you've built one, you've built them all, again aimed at money generation, slang "quick buck". If less people had bought that stuff, it may have had a counter intuitive effect.
I don't know anything about FC4, thought it was a joke at first, I read quickly about it a few weeks ago then forgot about it, thought initially it was a further development of FC3, you just reminded me it's actually a downgrade. I don't know the reason for it, but I would favor it's another vehicle for making easy money, since you're removing complexity which is always an easier path. I don't think they're doing it out of their goodness, to help the poor dears who don't want to deal with all the systems to alleviate some kind of moral dilemma, since most advanced models already are ready to fly, which I assume is what most people are interested in, if you want to get to a specific subsystem or armament such as in A/G, it's just a few additional button presses away. And in fact, in some ways, the F-18C is still at a very basic stage.
I agree with your comments about aircraft that were unequivocally deserving of further refinement, except you neglected to mention the F-15C, which although does not have a very pleasing cockpit to look at, it is certainly or originally was the flagship of all air superiority aircraft for the longest while, it was developed for the MiG-25, and indeed the other aircraft were developed for it. I think you wouldn't necessarily have to integrate all the IFF modes, to reduce development time and probably extreme, unnecessary complexity, but it's real role was just one, and that was to intercept, or escort, other aircraft. The current generation of Su's and MiG's especially with regard to their cockpit bear little resemblance to the original FC3 aircraft, probable lack of available information for these systems, displays and HUD, of course complexity (aversion to complexity), may have dampened or at least contributed to lack of enthusiasm for further refinement of those aircraft.