I am not sure about the Overstating.I think people have drastically overstated how much improvement is needed. I'd say it's more of a case of him needing to adjust to being a big fish in a big pond.
The only thing I find concerning is his knee but it's hard to tell when a player is at Dortmund.
Sancho looked quality for Dortmund and England but we have seen huge issues with him coming into the PL but we have also seen the Viking rip up the PL.
Sancho is a huge talent but 100m plus is still a hell of a lot of cash, and with huge wages on top of that.