Would it work if they just moved some stats from gear to the appropriate synergy crystal?
So have the top tier gear for pve and pvp be equal(hit AND valour) but dump a bunch of the appropriate stats for pve on its crystal and pvp on its. That way if you are maxed in pvp you can get into high tier raids, but have to wear 4Xpvp slots so you wont be BiS(so have less int/wis ect.). Also, pve players can use the gear that they worked hard for in pvp, but wont bis as they have to wear 4X pve gear and will be lacking in core pvp stats(end/crit mostly).
edit: and have vengeance scale equally or just get rid of it.