I don't this is stressed often enough. The only time we've seen legions "work together" in any sense of the word is the VIIth and XIVth Legions in 1.0. And by the end, Gaius was all but flat out countering Nael's plans by making sure the Eorzeans knew what Nael was up to. I wouldn't be all that surprised to find that the various Legatus are constantly trying to one-up themselves at each-other's expense (within reason). Or if things like the Legions in the border regions looking down on the Legions in the heartland and vice versa were commonplace.
At the very least, it seems as if the Legatus have a lot of freedom in how they run their legions (so long as they stay loyal to the crown and are effective at their job) and all the legions we've seen take after their legatus in one form or another. So far, none of the legions have been carbon copies of each other and I don't seen that trend stopping anytime soon.
