[Tuidjy]

Sinking 150 gems for a chance to destroy an enemy's capital is a no-brainer.
On the other hand, anyone who cannot keep a domain of 5 in his capital
deserves to lose it.

Furthermore, I would gladly give it a try even to kill whoever wields Mage
Bane, the Aegis, or the Stormsword. No, I have never had 150 water gems lying
around, but I would also never had 550 astrals lying around if I had not been
stockpiling them for an Astral Vortex.

In any case, the discussion is moot. Dominions II engine cannot comfortably
support this spell. If it makes its way into Dominions III, it would mean that
there will be a dozen other spells that will use the engine's new feature, and
then I am sure there will be counters. For example, if you do not want your
coastal capital sunk, raise the ocean floor of the neighboring province.