By your definition Eli Manning is now greater than Dan Fouts and Dan Marino. 
Next!
It's about a lot of stats... Should Eli throw more yards in his career or pick up some other records... He may be.
Winning a Superbowl isn't the only mark of greatness... There's a lot more to it... but it is "a checkbox" on the list of things to accomplish to be great.
It's just not required if you get to check off the rest of the items.