To correct and expand upon your point a bit. Yes, the Super Hornet isn't just a limited upgrade. The Super Hornet is a bigger airframe. You can think of it as

To correct and expand upon your point a bit. Yes, the Super Hornet isn't just a limited upgrade. The Super Hornet is a bigger airframe. You can think of it as "what would happen if we scaled up a Hornet by about 15%?" New wing. New intake design. It required a development program and a flight test program of a kind that you do when you make a new airplane, not upgrade an old one. The Super Hornet is much more capable. Greater endurance, can have an AESA radar, better ESM suite, better communications.