Sancho is a worldclass talent, he worths what he worths because of the player he is. if he was italian, chinesse or african wouldnt make a difference.
With Grealish we all know is not the same case, there are better players than him for that price. He has the "english tax" the same one we paid when we bought Maguire and the one we would have to pay if we wanted Maddison, Chilwell, Rice, etc any above average english is priced as top of the notch. There's a reason why the top clubs in the world dont have english footballers, its not lack of talent its simply theyre on the vast majority overpriced.