BV is very good, but opponents know exactly what's coming. It'll work at AP level, maybe even 6N, but the big boys won't be frightened of it.
Disagree. In 2013 game against New Zealand, when his game was much more limited, they still struggled to deal with him. Even if they know what's coming, as they did with Tuilagi, he can still be hard to stop. Everyone knows what Savea will do for the All Blacks; not many have stopped him. He was also voted England's forward of the Six Nations this year.
His main difficulty with England is being the only strong carrier in the pack and always taking static ball, so he is easily lined-up with two/three tacklers. When Easter and Attwood played in the Six Nations, and when his brother came on, he made lots of yards and half-breaks.
At Sarries he's in a pack with George, Mako, Kruis, and Itoje - a good set of carriers for the Premiership. Make that George, Mako, Attwood, and Ewers for England and he'd benefit hugely. Add Tuilagi, Yarde/Roko, maybe Brookes, and we could play Warrenball against the best of them.
As said by Raggs, a good England clearout would help too.