Watch our games, and evaluate our record with and without Carrick in the team.
Don't use a lack of replacements to cite why a player is so great. He can be important by default of that circumstance, but it is not related to him as a player alone. If youre looking at output of our first XIs, Mkhitaryan, Zlatan, Bailly, Carrick, Valencia are are key.
Oh ok, maybe we should stop looking at available players who could improve us all together. No fecking player arrives with a guaruntee label. What we do know is Nianggolan is a superior player to Herrera.
This wasn't a quote to my post, but highlights your lack of knowledge about other teams. Kante would easily walk into any team in the league and Chelsea weren't "torn" apart by Spurs. Did you actually bother to watch the match?
Also I hate it when people nit pick faults in other players and forget there are games where Herrera himself has been embarassingly anonymous.