Okay, here's my theory with the towers (specifically the big one in Garlemald)

As Urianger pointed out, being tempered to a nation instead of a primal is something we've never seen before. And then, we learned that the towers are summoning primals. My theory is Fandaniel and Zenos are trying to, or already have, use the biggest tower in the capital to summon the concept of Garlemald itself as a primal. A primal embodying the idea of Garlemald and what it stands for, explaining how people could become tempered by a nation. And then the beams coming from the smaller towers are broadcasting its tempering to other locations beyond its immediate vicinity.

I don't know how the Lunar Primals fit in, but that's what I think is going on in the imperial capital.