The F-4 was not technically unstable – rather it was nicely stable in the flight envelope it was designed to fly in - going to very stable in the supersonic part of the flight envelope. There are a few places where it is unstable but they are not in the design flight envelope. The F-4 was designed before the time of good Stability Augmentation Systems. The F-4 does have a Control Augmentation System but that is just to keep the stick forces down when in high speed very stable flight. It does nothing for stability.

The F-4 was not relatively heavy unless compared to a P-51 – it held over 14 time to climb and speed records and was successful in combat situations against airplanes of the time. There were design engineers, stress engineers and weights engineers that worked together to make each part only as heavy as needed to do the job. Because the engines were large and required a certain amount of fuel to do the missions required and since the airplane had to carry certain external stores, the airframe had to be designed to carry and hold those weights. But it was not heavier than needed to do the job. That it was heavier than a P-51 – sure. But the heaviness is not excessive to do the job with the materials and construction methods that were available.

The F-4 is considered an aerobatic plane by a lot of pilots that it shot out of the sky – it will pull over 8 gs in parts of the flight envelope. That will gray out most pilots just as quickly as a little Edge machine will. I have a photo of an inverted Blue Angel with the gear out in a demo - pretty good aerobatics. It rolls and loops. It was designed to be maneuverable within design limits that were predetermined by the armed forces paying the bills. That it can’t do a negative 8 gs or good snap maneuvers doesn’t make it bad - it was simply not designed to do that.

Do yourself a favor; before you shoot a shot across the forum’s bow could I suggest a few things. Try to be accurate - exaggerations don’t serve any purpose. Don’t perpetuate old wives tales.