Well, this is all just ridiculous.
Firstly, Hayne has shown more than "glimpses" in the years apart from 2009. He was a fantastic player in the years before then, and was an outstanding player in an incredibly shithouse team in the yeas after. In 2014, when we finally had a team that could win a few games, he won the player of the year award.
I will admit he hasn't shown more than glimpses since his return to RL, but was it because he was playing in a team that he didn't want to be in, or because he has completely lost the ability to play in that time?
Secondly, I don't know much about Union, but to say George Gregan is only famous because of one tackle is ludicrous. The bloke played for, and captained, his country for a very long time. He is considered among Union experts to be one of Australia's greatest ever players.
Lastly, Hewitt was world number one for over a year. He didn't just win one tournament. Admittedly, his was a style of game that wasn't going to be able to compete with the players who emerged just after him (Federer, Nadal, Djokovic). I guess he was lucky to find his best form after the old guard of Sampras, Agassi but before those other guys.