I suspected something like this would happen, that it would be one kind of reptile or another.

Because...what's the point of a dragon auspice?

Auspices are special because: They live a long time, they're smarter than regular animals, and can become very powerful over time.

Dragons...have that already. Dragons in FF XIV are not just big lizaards. They're very smart and, if they live long enough, become very powerful. At that point, why not have an au ra become an auspice?