He'll never improve a bad playing team, his form is directly related to the team itself. If the team plays well, he'll do well, but he wont carry it. We allready got Pogba who doesnt remotely carry the team, and heavely depends on Marchisio or Khedira.
Last season, he was ridiculed for his poor form. Season before he was interesting cause of good form.
See, if you struggle against a big team, this is the type of player that wont deliver, but he will do when you are domminating the play. Considering juve this is tricky. We need a core of players that carry the team, life players around them above themselves.
Pirlo, Vidal, Tevez, Marchisio are/were all players whom had that characteristic.
Now such players are interesting if they have magic to decide a game on their own, or if they just become that damn good if you are domminating. We got such player, Pogba.
This is why, we'd want Gundogan, not mkhitaryan. Sadly, so do richer teams.
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Put it like this, if you got far to many mkhitaryan, and to few marchisio , you are the blueprint of a choker team