I guess I am somewhere in between your position and that of some of the others here.
If you are talking pure, inate talent, it is possible that there are 15 or 20 riders better than Nicky. There ARE a lot of very talented riders out there, between 125, 250 and MotoGP, WSB and the various national superbike series (eg AMA, BSB etc). However, many of these extremely talented riders will not, or at least have not yet, proven their ability to translate that potential into significant race wins.
Success also depends on psychological and other personal factors. It depends a great deal on strategic thinking, good decision-making, self confidence and extreme concentration. Look at all the young hotshots that come on the scene with great lap times, only to crash and burn (often literally) under pressure. Look at all the times that Rossi was 3rd or 4th in qualifying, sat back in 2nd or 3rd for much of the race, until the leaders eventually cracked under the pressure and made a big mistake, "handing" Rossi the win. That is not Rossi's luck, that is his mental toughness, and the relative lack of same on the part of most of his competitors.
For a couple of examples of very talented riders who fall down (literally and figuratively) in this dimension, I would cite Checa. Very fast, very exciting to watch, but has not yet proven his ability to win consistantly. In WSB, Rueben Xaus seems to fall into that catagory.
Until this past year, I would have put Alex Barros there as well. However, he seems to have reached deep down and found some toughness, and finally after years as an also-ran, is argueably best in MotoGP today.
This is where Biaggi falls down, in my opinion. He probably is at least as talented as Rossi, but somehow Rossi has found the way to mind-f#ck him, both on and off the track. Until Max figures how to deal with that, he is destined to be beaten on the track.
I ink this is where Colin and Troy will really shake up MotoGP this year. It is not only because of their raw talent, but also because, in my opinion, their guts, determination and racecraft are much better than that of most of the very talented MotoGP regulars. Rossi will not be able to mind-f#ck them like he does Max. If Aprilia and Ducati can deliver bikes that are even CLOSE to the Hondas and Yamahas, they will be fighting and clawing for the podium.
Nicky seems to have the kind of personality to not let himself get beaten up mentally. He certainly has worked his ass off in all the trials. It actually may work to his advantage for everyone to now have lower short-term ns of him. That will give him the opportunity to learn the tracks, learn his competitors, learn about life on the international scene.
My guess is that Nicky will not get on the podium this year, and that he will generally be back around 10th place, more or less where Hopper was last year, but at the same time, it doesn't seem like too much of a stretch to see him up there later in the season.