Some interesting views expressed above.
In my opinion, it is going a bit too far to class Rosberg as 'an average driver'; but I would agree that he is not quite a top flight driver, and somewhere below the likes of Alonso, Button, Hamilton and Vettel.
Webber had a poor season last year, which has somewhat reduced his stock; but despite machinations behind Red Bull's closed doors which suggested to me (and still do) that Hell's Mutt Marko is happy to see the Aussie fight his own corner with far less support, he is also probably sitting below the top flight. Rosberg and Webber are very different characters and at different stages in their respective careers but there are similarities in what they are ultimately likely to achieve.
Further opinion: For what little it's worth, I feel Webber would out-gun Rosberg if they were teamed together.
This places Rosberg somewhere around sixth best at the moment - and despite the shifting sands at Mercedes, I still have him as their best driver. Therefore the argument that the car could be better than it looks would seem valid.