I'd imagine that the first one to summon wins, so if others attempt to summon they may end up wasting the attempt. I"d imagine that every primal will pretty much do an OPed 9999 dmg strike to target in range. Since from the current setup you not only have to defeat the primal but you then have to harness they ability to summon in which may be a challenge in itself. So the idea of summoning it would prolly be in a situation in which you don't have the upper-hand and "need" to use it.

It may also be tricky to pull off in terms of PVP, if groups become aware of the free company that has the primal they may avoid fighting those people to avoid an auto-loss, or perhaps they would want to challenge them to force them to use the Primal so that they can claim it for themselves.

I'd imagine depending on the radius of the Primal when fighting in a pvp against a group with a primal the best idea would be to move in 2-2-2-2-2 formation and making sure your forces never group up together, if one group is being attacked in 6-2 match have those 2 retreat and see if another 2 can intercept the enemy and bind/sleep them to even the odds.

It will be interesting to see how things flesh out though, if they actually set it up where if 2 groups in pvp are able to call their Primals and duke it out, it would make thing interesting. Though we also don't know the exact time/people it takes to summon the primal so it might not be that easy. It could take 3 members to summon plus a 30 second period of standing still as they perform the incantation while the other defend them so that they don't get interrupted.