He is our number one playmaker. His job is to create opportunities for the striker. He's not in the team for anything else. If all we required from him was to do 'the other things' to an okay standard, then we might as well play JWP or Davis ahead of him, because they - certainly Davis - do the other things very well.
So there is no point in him playing 'okay', if he is not doing his primary job. He should, minimum, be creating 3-4 goal-scoring opportunities for the man up top. But he doesn't any more. He has lost his knack of picking out the killer pass. The entire season, and last, the fans have been complaining about lack of service for the strikers. If Tadic isn't to blame for this, then I'm not sure who is.
If we were top-half, I'd say he is a luxury we can afford to be patient with, but as we are fighting relegation, I just don't think we can afford to have him in the team, and that we should start looking to the grafters to fight our way back to safety.