Well, here's the main thing...a complex campaign system does NOT require complex avionics system modeling.
You could take TK's planes, terrain, modeling, etc and mate it with an F4-style campaign and it would work. Likewise you can take a plane as complicated as the one in F4 and give it a bare bones SP/MP game to go with it. In fact, it was done, and it was called Back to Baghdad. Anyone remember it? No? That's because it was like flying a REAL F-16 simulator. All the switches, bells and whistles, accurate systems and all, but outside the cockpit was NOTHING. Horrible terrain, AI, campaigns, etc. Oh, and it was $100.
I'm not saying it doesn't cost as much or even more to make a fancy campaign as it does to make fancy systems modeling, just that a fancy campaign does NOT require the "study" that advanced systems do.