I'm not ruling out that Contador would have been competitive or even won Il Lombardia in his prime if the route had already been harder at the time but I feel like this is ignoring one of the main weaknesses Contador had, being that he wasn't very good in long races. Tbh, this is a trend that wasn't really noticed until the latter stages of his career so maybe he only lost the ability to compete in very long stages when he got older but I'd argue this weakness was probably there all along, it was overshadowed by him being so much better overall that you didn't really notice.Contador was never gonna be a prolific one day winner cause he lacked the sprint and wouldn't really destroy everyone at <5 minute climbs. Also at the peak of his powers Il Lombardia was much more of a puncheur race.
But at least from 2011 onward the trend that he performed way better in short stages was definitely there.
So while this isn't a very obvious weakness, it would be a very good explanation for his lack of classics results.