And that's why the choice of player for the other advanced midfielder is difficult and depends on the game. If we're in possession with a 4-1-2-3, a player like Marcondes or Stanislas would definitely be preferred, but if we're out of possession a player like Cook or Pearson makes the 4-3-3 more solid than having Lerma be the only of the midfield three with any defensive nous (Marcondes was brilliant today, no doubt, but how often did you see him make a defensive contribution?). It's situational and not as clear as some of your "put Marcondes there plzzzzz" posts suggest, though I agree he's a great option for games where we dominate possession and are trying to break down a tough defense.
And then we have the long term strategy of managing player fitness by rotating where he may be used as a Billing replacement rather than playing together. We can say "they're professionals and should be able to always do the full 90 no matter what, so this is a non-issue", but if that's not reality then the real situation must be dealt with. I'll trust Parker to be a better judge of this than I, seeing as he's with them daily during training and I'm not.