I think his move to Chelsea reduced his playing form because the Sancho I knew that played in borrusia dortmund was an entirely different person as he was so in check with his playing style and also help the team in terms of goal but for now I think his form has greatly reduced and that deal is a really good deal indeed and who knows maybe he might get more playing time over there in Italy because that's what really going to help a player back in form.
Actually before coming to Chelsea is form already declined and he did better for us than Manchester United. His stat in the loan spell at Borrusia dortmund wasn't that good compared to his past stat the club. Also, the Bundesliga is less tasking than the EPL, how many players can you think of that couldn't perform well at the Bundesliga but did well in the EPL?
Don't speak as if Chelsea was the reason he declined whereas he was having a better performance there, trying to get back on track.