Simple question; when was it?
Did Leon ever have a prime as a professional?
This is probably going to sound crazy, but I believe that beating Ali after only 7 fights was the worse thing that ever happened to Spinks.
Yes, he can tell his grandchildren that he beat the greatest, but at what price?
I think that taking the Ali fight & ultimately beating Muhammad thrust Leon into the big time way too early into his career, thus he never learnt his craft properly.
I'm not saying that he would have been an ATG, but I do believe that he would have achieved a bit more in his career had he not fought Ali so soon.