So hey, new idea that almost makes the purple sun plan gain traction with me, only barely failing because I think the dragon plan will win anyway, because the dragon plan is really cool, because it'll still work way better against any sort of tunneling or underground target, and because if I wanted a Purple Sun I'd just try the cheaper method of hiring a battle wizard:
Wouldn't a Purple Sun also be great against those dragon Ogres we passed on the way here?
I've been thinking that that was too interesting to never do anything about it, so they're likely to become relevant to us eventually, and a doom stack of Dragon Ogres in Total War Warhammer apparently kills absolutely everything, so I'd expect them to be a terrifying field army.
If we're talking utility against the Dragon Ogres...
The Dragonification Altar is unique among proposed anti-dragon systems in that it is capable of projecting power.
Purple Sun, Chain Lightning, Bullet Hell, all static and limited to the K8P region, probably only part of the K8P region. Even if you build them as battle altars with intent to deploy them they have to get LoS, so they're not all
that useful - you have to treat them basically like classical artillery and protect them from counter-battery fire and so on. Runic artillery has all the same problems but even more so.
A dragon, on the other hand, can fly quite a ways and then do quite a bit of damage before its timer runs down and it has to return. A small task force can move relatively quickly, strike from a distance, and return once the dragon completes its assault. The altar and its operators don't have to expose themselves to attack, and if they're rumbled before or after, a dragon is better at stopping a charge than a lightning bolt is. All of this means that it's possible to deploy the Dragonification Altar on offensive missions.
The Purple Sun tower is like having seeded your countryside with nuclear mines: Wipes out anything that attacks, but has a nasty tendency of also wiping out you with them. The Dragonification altar is like an aircraft carrier strike group: Primary use case in an all-up war is to blow up enemy fleets, and it's slightly less scary than a nuke, but it's also far more precise and you can use it to launch offensive missions when it's time to attack.
The best way to defend yourself from an attacking army is to hit it and destroy it before it's an army. Or to blow up its logistics. Or to force it to hunker down and defend its own territory instead of striking at yours. The Dragonification Altar, being able to project power, can do all of those.