He's still arguably the best fly-half to play the game along with Carter if hadn't missed every international match between the final and 2007 6 nations when he was aged 25-29 due to successive injuries we might have a far better idea on how to compare the two. Its scary to think the impact he may have had if he'd actually played regularly in his prime.
Its worth noting he did play in 2005 Lions tour but was injured after the first two tests and was the only international rugby he played in that time period.
Jonny Wilkinson. No, not really.
To be known as the greatest flyhalf to have played the game you'd expect some obvious outstanding qualities related to the skills of the position. These would be :in attack, 1. dangerous ball carrier in own right, think Jonathon Davies for example. 2. supreme playmaker in both set and open play, organising backs and forwards in attack. In defence: a safe and punishing individual tackler. The flyhalf channel is often a target for attack because F/Hs are traditionally soft in defence, but not in Carter's case. Lastly, an accurate 2 footed long punt (or chip kicker), in either attack or defence.
Goal kicking or drop goal kicking are these days coincidental with the position. Any back can kick field goals behind a ruck or maul and any of the 15 can place kick, think John Eales for example. It isn't a core F/H skill.
Wilkinson was not internationally outstanding in any of these core F/H roles and for most of his career, rarely threatening the line with ball in hand and was very often targeted because he was a relatively weak tackler. His fame remains connected to that ice cold drop goal in the WC final. Even his goal kicking, at around a very respectable 80% success, is not better than innumerable others. His reputation, while huge in England, is pretty much absent in other Rugby countries because he really wasn't a threat at the highest level. It's always an interesting thing to imagine, or actually watch, a players highlight reel. In Jonny Wilkinson's case, if you remove key goal kicks and drop goals, it would not give many clues about why his reputation remains so high, even in England. But he did drop that goal!