The F-20 came along long after the lightweight fighter competition that resulted in the F-16. What makes you say it was a "much more capable fighter"? Seems to me it carried an inferior radar, carried less fuel and ordnance, and had the same narrow performance envelope that the F-5/T-38 did.Or maybe make smarter procurement decisions. A famous one would have been taking the F-20 over the F-16. A much more capable fighter, but since it looked like an old F-5/T-38 it was nixed.