Before taking charge at Juve, Conte already had about 4 years coaching in Serie B. He lead 2 different sides to promotion. I would hardly call him an amateur when he joined Juve. The Serie B is pro isn't it? Someone like the current guy at Inter could be considered an amateur...he's only coached youth sides.
As for unproven...maybe...it's arguable. For me...leading 2 different sides to promotion isn't unproven, but I can see how someone might disagree. Unproven, doesn't mean amateur though. I think someone like Ranieri could be considered unproven.