What? Fellaini is twice the player Herrera is and I don't even think Fellaini is anything special. This was my opinion even last season despite Herrera getting all the plaudits (let's not get into that).
Firstly, this was a cameo and Fellaini was thrown into the deep end while clearly not even fully fit. So saying that it is unfair for anyone to defend Fellaini, a late unfit sub and slating Herrera, a starter for the past few games, is pretty much off the mark. Not being Zidane or Iniesta, of course Fellaini couldn't cope with it and made mistakes. But in the end, he did whatever he was asked to, fairly well.
He will always be average and sometimes do stupid things like giving away a penalty, etc, but the good things he does as a squad player will outweigh them. More importantly, he contributes more to the attack than Mkhi or Herrera ever would.