I want to talk about tempering

[Vulcwen]

But... if vanquishing a primal returns its aether to the land, then something like the Burn couldn't come about as a consequence of summons... right?

Well, it could be that the aether moved to other parts of the world. A land drained of aether can't support the lives of a primal's followers, meaning they'd likely have to move to other places, and the primal would move as well.

[Cilia]

Well, it could be that the aether moved to other parts of the world. A land drained of aether can't support the lives of a primal's followers, meaning they'd likely have to move to other places, and the primal would move as well.

That makes sense, but... while it's not a fully documented thing, unless they're ensnared by something like an Allagan restraint a primal is typically brought down very near where it's summoned, and not (terribly) long after. Those aware of what primals do to the land will kill them, even at great cost, so a primal surviving long enough to drain all the aether out of a given area seems... unlikely. Repeated summons could do the same thing, but given we've seen an upwards of a dozen primals summoned in the past 1-2 years (story-wise) with no visible detriment beyond Bismarck literally eating some floating islands... that's kind of a tough sell. It would have to take dozens and dozens, if not hundreds of summons to produce something like the Burn...

The idea of primals leaving their point of origin and their followers trailing after is an interesting idea, though. Perhaps that's how Eorzea became Hydaelyn's locus of aether?