Certain players thrive in Germany and struggle more in England. Sancho seems like one of those, although to be fair he was looking much better towards the end of the season.
I doubt we're after him, though if Emery thinks he could get him back to his Dortmund form, we're talking about a potentially world class talent.
More likely we'll go after an Iberian / South American based player who will give us similar traits but not murder our salary budget.