There have always been so many different methods to dealing with a 'summoner' class across the Final Fantasies.

In some, you summoned that avatar/primal/aeon/whatever for just a few seconds, it did a powerful ability, and left. Carbuncle obviously won't work this way (because of the ability to let him tank, which was mentioned), but none of us are sure about the others. Would the elemental avatars work this way?

In FFXI, you summoned an avatar and spent mana to keep it out as well as mana to use its abilities. If you ran out, or you chose to dismiss it, it would leave. While it was out, it acted as its own entity. Although friendly PC's could not cast on your avatar, enemies could, and so your avatar was efficient at tanking or absorbing abilities (like 1k needles).

In FFX, a summoner became immobile while you, personally, controlled the aeon. Yuna would sit on the aeon or stand next to it... sometimes even run away if it was so large. While your aeon was out, it took all damage for you. None of your party was harmed, and neither was the summoner. What if this is brought into play somehow? (You summon an avatar and gain control of it, but also are forced to be near it, or stand on it.)

Going from the concept art alone, it seems as though the essence of the avatar is summoned specifically from a book. This might be misleading simply because all we have to work with is the concept art, but it is something to consider. The essence seems to be coming out of the book, and perhaps it is only but a fleeting moment that passes while that essence is summoned and maintained?

We really can't know for sure.

As an answer to people who replied to my previous posts: I definitely agree that some giant/gigas race would definitely worship Shiva. The reason I didn't consider them is because there's been no info released about those. I believe I saw the concept art of the sahagins long ago, but simply didn't remember them because they look very different from what I'm used to. To the person that said the beastmen I mentioned aren't aggressive: No, they are not, but at least some of them WILL be in 2.0. I was personally part of an event where goblins attacked the city. (Keep in mind, when they were spawned, they were still green, but we were urged by an NPC/GM to kill them. I'm pretty sure they were green then only to make sure they didn't maul low levels. After the final save, all bets are off.)