I do see your point of not using companions as a side-kick. But the option not to summon them is there. Send them on craftings/missions while you and your friend can enjoy the gaming experience.
I for one love the fact that there´s a companion there to back you up. I can now choose to focus on a healing class with some support abilities, while my "side.kick" kicks ***.
If we were to compare this game to another MMO not using the option to have a companion by your side. You wouldn´t be able to mainly focus on a healing class (as easily). You would be forced to build a DPS/levelling spec and then after hitting cap spend money to respecc.
WoW for example has another option. They´ve made it so that you can have two speccs quite early in the game. Making it possible for you that wishes, to play a class that´s able to heal/tank and DPS.
I find that the way BW has approached this, is quite unique