There is probably an argument for making Arena specifically, a separate e-sport game, with a WoW theme.
That said I like having Alterac Valley in the game since the sheer number of players tends to mitigate the PVP god-gear players somewhat…some of the other BGs can be fun…and I thought the Xpac-specific Battlegrounds like Wintergrasp, which was linked to PVE mat gathering, were both enjoyable and gave PVP a purpose within PVE…again sheer numbers helped, if you were short on PVP gear.