For me the benchmark for a new signing has to be one thing - "Would this player start for any of the current top 6?", not just "Would they improve the squad?" This is why I'm absolutely not having these Amavi/Pickford etc. shouts.
For example, Coleman would start for City. Gueye would most likely start for Spurs, Schneids for Liverpool, Lukaku for Chelsea etc. hey ho, lo and behold, those 4 happen to be our best players.
Would Mirallas start for a top 6 side? Funes Mori/Williams/Baines? Not a chance. So we need to replace them, whether it's with established quality like Van Dijk or outcasts from the other big clubs that could come good - Alderweireld, Schneids etc. This summer is where Walsh really has to start earning his badges.