No, rated PvP just needs to not be focused entirely on 3v3, PvP balance should be on larger group combat.
Rated Battlegrounds should be where PvP balance is focused, because then not only would the focus of rated PvP be "balanced" but so would unrated battlegrounds, which is where the overwhelmingly, massively, vast majority of PvP in this game takes place. A decent middle ground, if they want one I guess, would be to scrap 3v3 and bring back 5v5, use it as the focus of PvP balance and use it as the primary arena tournament format.
Either way, very small group PvP is an extreme minority and there is no reason at all it should be the focus of PvP balance.