You failed to read the rest of the things Yoshi's said about this system. You don't simply get to summon the primal right after killing it, you have to get a card. The free company which kills the primal AND gets the primal's card (which I'm assuming is a low drop rate) will then get to summon it whenever they want and in any setting, and once they use it they lose the card and have to re-farm it for that primal, since only one card is dropped per server at a time.

Obviously, many free companies will try to gain control of all the primal cards and hold them all at once, and if they choose to never use them then that's their choice. I assume most companies will decide to eventually use their cards in GvG content since it's basically an 'I win' card.