Jerry's legacy will be that as a professional football businessman and owner, he changed the NFL forever for the better, and was one of the main catalysts who led the NFL into its pro sports dominance in the 21st century. He revolutionized advertising revenue and made owners see the value of their product since he showed how you could take full advantage of your team's popularity in sales. He showed how owners could take what used to be side business, control them from the franchise, and turn them into money making legacies. Everything from concession stands, to stadium events, to team TV networks. He will remembered as a great businessman who took a franchise that was leaking millions of a dollars a month and turned it into the most efficient and valuable pro sports franchise in the world. FOX NFL, NFL Network, Pro Apparel Shops, Madden, Super Bowl Commercials, so many things that are standard now they may not have come along as much as they did without Jerry Jones leading the Owners and the NFL.
As a GM, hey, at least he could produce some winning seasons. That's about all I can say.