I think many, me included, will have to understand that the second we are going to judge him based on anything beyond his basic tasks (ball recovery and passing it to the nearest teammate) we are going to be disappointed. It's clear the guy has heart and is excellent in this role.
The problem I have with Bentancur is that he does everything in one tempo. There is no acceleration in either passing or off the ball movement. Today, around the 90th minute there was an instance Atalanta lost possession in midfield and instead of just pushing the ball forward to a free teammate, I saw him take 2/3 excessive touches, ultimately leading to Atalanta closing down space and Bentancur just giving a backward/lateral pass. Another moment where we had a great chance to counter (3v3), and instead of passing it diagonally in space towards Chiesa, he gave another sloppy lateral pass. If executed well, things like these can win you games. The other day I saw Modric and Kroos vs Inter, completely dominate midfield for 90 minutes straight by simply passing the ball over the top from side to side and utilize space. Often Bentancur's passing is just sloppy, unfocused, and without finesse.
Having said that, from our current midfield Bentancur is probably the last or second to last to be replaced IMO. If we can get someone like Pogba in January and pair him with Bentancur/McKennie and Arthur, I think we'd be at least in a position to compete for every title this season.