Yes, he was an excellent 1-day classics rider and won the World Championships in '93, but that is very different than being able to excel at a 3 week tour. He climbing and time trials were mediocre prior to his full-time contract with Ferrari.
I'm not certain that one classic win (and zero monuments) entitles you to call him an "excellent 1-day classics rider" - although one of the races he did win prior to 1998 was the Clasica de San Sebastian, a well-known climbers race.