It’s a laughable assumption/ assertion anyway.
When Lacazette wasn’t playing well no one was saying hey when we sign Aubameyang he can come in and show him a thing or two. If we sign a new goalie or CM it wouldn’t be to show Cech or Xhaka a thing or two. It would be to either replace them or rest them. Coaches are the ones who are primarily tasked with improving players, and setting the tone. Not some random old dude from another club who has no standing in our dressing room and isn’t exactly a colossus in his position on the world stage.