Had 12 round fights been brought in sooner would Hearns be Greater than Leonard

[Snakey]

I've always said that Hearns was good chin short of being better than Hagler and Leonard - and that his long legs let him down by going to jelly when he got hit.

Somebody (Stebs) on the other Hearns thread mentioned that Hearns was well ahead after 12 rounds of the first fight with Leonard, and I think there is little doubt he won their 2nd fight.

So if 12 round fights came in sooner, would history have Hearns above Leonard in the all time great stakes?

I think the answer is YES

You train differently for different amounts of rounds. What you are saying actually can not be proven because Leonard could of changed his game plan for 12 rounds and beat the shit out of Hearns.