Apart from his crossing I don't see how his forward play is going to make this staggering difference some claim. The crosses are nice, mainly when Cavani is playing, probably less of a factor otherwise.
But other than that he's neat and tidy but hardly the most dynamic player in the world. AWB has a lot more pace, if we could coax him into making more runs without the ball that would allow Sancho more space. Or if they want to let AWB go then he may get plenty of open space to get into more dangerous positions as well now there is as bigger threat from the right flank, potentially. Mason is still very much learning the game, the runs, the positioning, and can be quiet which makes the job harder for a full back.