At first it was "clear" that Mr. Robot was a delusion because only Elliot seems to talk to him.
Later that was broken, as we saw him talking with other people apart from Elliot. Then it was argued that it's part of Elliot delusion, it's Elliot really talking with other characters and him imagining it's actually Mr. Robot.
Then we see Mr. Robot talking with other people even without Elliot present, and now it's argued it's Elliot doing the talking but it's a case of split personality, sometimes he is Mr. Robot and he acts like Mr. Robot, other times he also acts like Mr. Robot but a part of him still acts like Elliot is present.
I mean, it could be, perfectly. Yeah, I also watched Fight Club. But I see a clear... movement in the goalposts.
Whatever it happens in the series, it can be argued it's Elliot's imagination, the series uses an unreliable narrator, etc.
But where does it ends? Shit, maybe all the FSociety characters are a figment of Elliot's mind and he is lone hacker all along, and each character represents a piece of his psyche!!
Who is the super ego, the id and the ego?
Uh? Obviously all Fsociety knew who was Elliot before Elliot knows of them. They got in contact with him. They tested him. They messaged him in the server, later they got in contact physically.