Nobody says, that the results of the team are the only thing that matters. Of course not. A team has better and worse players.
Guys like Bale, van Persie, and Suarez or DDG have been absolute stand-out performers in their teams and everybody recognised that.
Herrera is nothing like that for us, even if you take only a few month of this season into account. If we had to argue about who our stand-out performer is, it has to be Zlatan. Maybe you could make a case for Micki, but he missed too many games. After these two players we have 5-6 players (Vallencia, Bailly, Carrick, Pog, Herrera, DDG) who are *roughly* on the same level. Even guys like Mata or Rojo are doing alright. You can make a case for or against any of them, but I don't think that any is really standing out. If I take Herrera's complete career in Manchester into account, the whole thing looks a lot worse. He wasn't even a nailed-on started till the start of this season.
On the other hand Kante is going to be the dominant midfielder for two title winning teams. He wasn't the best player in these teams, but he was vital for both of them. That should tell you something. Not a lot, but something.
Following the caf love-ins of certain players we'd have a team full of worldclass players, because Martial, Pogba, Mata, Di Maria, Schneiderlin, Shaw, Jones, Smalling, Rafael were all considered to be world-class in the making. Herrera is just another one in a list of names, who gets overhyped after playing good for 5 month.
Herrera is a very good player, but if you look around in the world of football, there are a lot of players around his level. Nothing wrong with that.