Indeed he has. And he himself said that he believes he's a top six batsman, when we signed him.
But the facts are that this season he averages 21.6 with the bat, which is less than even Briggs (and less than Dawson, by the way), and 28.9 for his whole FC career. Two centuries in 123 innings. Dawson has three times as many.
The only way that we can realistically put Berg at 7, in my opinion, is when we have the top 6 firing and Wood coming in at 8.
Wheater is also not good enough to bat at five in D1, in my opinion, but that's another issue.