That was his role though. At the time he was at his peak, that's how the game was generally played. He changed the game so that you needed a good kicking fly half, someone who could kick for field position well, and kick goals. And he was the best at it.
But it's also naiive to say that's all he can do. While he was never exactly a Dan Carter with the ball in hand, he was still pretty good. Aswell as winning the WC final with his boot, he also set up Robinson's try with good burst and perfect pass to put him into the space, I also remember a fantastic try the year before to beat the All Blacks at Twickenham. But in open play he was best at defending. An excellent tackler and that's why he always got injured. Never afraid to go in hard for big hits against much bigger opponents - an amazing try saving and ultimately world cup saving tackle out wide on Lote Tuqiri just a minute or 2 before the drop goal springs to mind.
IMO when you say someone is one of the best players of all time, they have to have changed the game in some way. And that he did. Now that sort of game is frowned upon due to the recent emergence of the running game, mainly sparked by the All Blacks and in particular Dan Carter (who also deserves to be mentioned as one of those players who has changed the way the game is played). Wilkinson's game has been phased out and now there is a new generation of rugby which favours more running than kicking, and more going for tries instead of kicks. Wilkinson was the best player of his generation and I'm looking forward to seeing how he can get himself into the latest generation (if that's the right word to use).
Don't get me wrong, I don't really want to make it look like I actually know anything about rugby, this is just the way I see it. It's naiive to dismiss Wilkinson as overrated or crap just because "he only kicks the ball." That's how the game was played when he was at his peak, different periods lead to differing types of games and his game is not what is played now.
As for the overrated comment, overrated IMO means someone who is hyped up as the greatest thing since sliced bread, but never really lives up to it or achieves anything. I don't think Jonny Wilkinson can be described in this way given as I said before he pretty much single handedly won a world cup, a 6 nations grand slam, and also became the top point scorer in the history of the game. I don't feel it can be argued that he never lived up to his promise, what more in the game could he possibly achieve?
'Overrated' is word I would use for say, Gavin Henson the welsh player. He kicked one goal against England and ever since he's been hyped up as the greatest player ever to have graced the game. From what I can see, he's nothing more than a big ego with a fake tan, a bad haircut, shaved legs and the obligatory celebrity girlfriend (or perhaps she dumped him recently, I'm not entirely up with this type of gossip). He was absolutely terrible on the Lions tour here last year and I think his comments that I remember seeing on TV after not being picked for the 1st test summed up his character perfectly. Something along the lines of "I'm devestated. It's absolutely disgraceful that I'm not in the team, I should be there and they don't stand a lot of chance without me." (not an exact quote, but it was along those lines) I don't remember any sort of comment wishing the side any luck. He got his way and was picked for the 2nd test. He was the worst player on the field and was subsequently dropped for the 3rd - he did pick up an injury, but wouldn't have played anyway. He's a mediocre player who will be living off that one penalty against England for the rest of his life, having achieved not a lot more in his career IMO.
Note: Then again, I'm far from a rugby expert and don't claim to have a lot of knowledge on the game.