Two points:
1. His stats were just very good for the period that he played in; however, especially by today's standards he's definitely not Hall Of Fame material.
2. His election into the Hall Of Fame was a combination of his stats and his contribution to the legitimizing the AFL-NFL merger. Probably no one player had a bigger impact on the evolution of the NFL than Namath. When the merger was first agreed to, everyone just thought that the NFL teams were far superior to the AFL teams, etc. His Super Bowl III win gave instant credibility to the AFL (and the merger); and that was a "really big deal" back in 1969.
The merger had many fathers: From Pete Rozelle, to Joe Namath, to Lamar Hunt. The list goes on.
How can you talk about the rise of the AFL and the merger with the NFL without mentioning Joe Namath? The iconic Jets quarterback's flashy style, star power and big arm gave the AFL unimpeachable cred. Namath explained to Jeremy Schapp that his iconic finger point to the sky after Super Bowl III victory in 1969 described not just the Jets' rise, but of the AFL's new place in the professional football pecking order. The league's merged one year later.
In 1969, the New York Jets defeated the Baltimore Colts and Super Bowl III was one of the most pivotal games in NFL history. What if the Jets lost?
thecomeback.com
The Jets winning Super Bowl III helped make the AFL/NFL merger go smoother and made Joe Namath a Hall of Famer.
Having said all that, the biggest thing that would’ve changed had the Jets lost Super Bowl III would’ve been the NFL itself. Before Super Bowl III, the AFL was viewed as an inferior league from many people. Sure, the AFL and NFL merged but the NFL didn’t really take AFL teams seriously. Many of the players on AFL teams were cast-offs from other NFL teams and were put on teams that formed at the start of the decade. And two of the best teams in the AFL were blown out in the first two title games. Of course the NFL didn’t really respect the AFL.
Another NFL win in Super Bowl III would’ve meant passing a point of no return in terms of equality between the AFL/AFC and NFL/NFC. The merger probably would’ve still gone through, but the stigma of the original AFL teams would’ve resonated for a very long time. Those eight teams would’ve been in the NFL, but they wouldn’t have been seen as “NFL teams.” Would those teams have remained in the NFL after 50+ years? It sounds unthinkable to consider but if the Jets hadn’t won Super Bowl III, the entire fabric of having the same 32 teams likely would’ve been altered and football being the most popular sport in America arguably may not have happened.