More discordant than the fact that he has completely implausible conversations with everyone but either everyone talks to him and he never talks back or provides input or as much as acknowledgement that he hears them, or conversely, if the player simply talk back to them in his head, the fact that no one says anything back to what he is saying?

Role playing a video game character does not work until artificial intelligence matures to the point that a computer might have a meaningful conversation with a man.

The idea is that the player fills in their response in their imagination. Though, I think it's a little fourth-wall-breaking when NPCs comment on the player's silence. No future-AI needed.

I know, but as I said, the n.p.c.s don't respond to the player's imagined responses so it doesn't solve the problem that he conversations are implausible and silly.

Either the player doesn't imagine a response, and the n.p.c.s are talking to a wall and act as if that be normal. Or the player does formulate a response, and Gordon Freeman is talking to walls, and acts as if that be normal.