Never said he wasnt a good rider. He allready is a great rider. And I would be happily surprised if he managed to win one, after all Oscar Pereiro won the tour to...
Just some small details are lacking that I feel are very hard to overcome for riders with GT ambitions.
He seems to struggle badly when faced with true 2000m cols and good opposition. With all his talent, he should be doing better, but I feel that the gap between his current level and whats required is huge. Even more because the parcours these days tend to go for more climbs, longer, steeper, more top finishes,... and minimum TT.
And secondly in the limited longer demanding tours he has ridden he tends to fade or have a day off. Might be the age, but it is something that true grand tour talent tends to have from a young age: the ability to stay strong when others fade after days or weeks of serious races.
Winning a grand tour is about perfection, having no weaknesses, and his current weaknesses are in the most critical areas for a GT winner.
We've heard it all before.