I would say he's proving to be the ultimate "good times" player. He can be brilliant when his team is brilliant, but is piss poor when his team is not playing well. Now this isn't a huge knock on him as the vast majority of players are like this, however when looked at from the context of the most expensive player of all time it speaks volumes. A player (especially a vital cog in the midfield) should be the one digging in and driving his team forward out of those stretches of bad play.
All three of Marchisio, Vidal, and Pirlo were like this. They do so in different ways, each one of them, but they all elevate their games when Juve is/was going through rough patches of form and they all make their teammates perform better.
Pogba is the exact opposite. He is far too individualistic, especially when things go poorly, and while this is not a problem with a CF who bangs in goals, it is a big problem with a CM. He stops passing to certain teammates, as though he doesn't trust them, he throws little tantrums on the pitch, he dribbles a player or two and then gets dispossessed by the third instead of making an easy pass. When our team was looking terrible to start last season, and the same deal with ManU to start this season, Pogba does the exact opposite of being the leader on the pitch that elevates his game and those around him. He most often looks like he's playing his own little game, that has nothing to do with the rest of his teammates.
Until he learns how to step up during these rough patches, he'll never be anything close to a 100M player.