I see your point, but considering what he has already done at this stage of his carrier I would not worry too much.
The player he actually reminds me of at similar age is Eden Hazard. But I do think Eden Hazard, due to his build, was maybe an even bigger talent. An while Hazard was one of the best player of the past decade in the PL, I actually feel he could have made even more from his talent. I think we have gotten very used to seeing players like Mane, Salah, Sterling, Sane and Rashford, left striker kind of wingers, and therefor thing of these as the blueprint for a winger. Sancho, in my opinion, will be more of a playmaker type. A player who drifts inside infront of the defense and creates, but who also can and will take players on and move into the box.
I think that will suit us. Rashford is verand Greenwood will be. We need someone who can find them.