Well, for Dark Vortex you get an attack that can allow the Hero to strike the enemy down even if cornered, it costs less (and those 2PsP points can make quite a difference), hits the same number of tiles, allows the Hero to attack unit formations from any side of the map with ease. (Say, if the enemy comes up too close, and the Hero is located on the side of a map, then the enemy will be out of Light Bomb range- great example is Dean Lucas from TRPG2 battle.) Also, the attack deals more damage on the same level.
About Pyro Hail I do agree completely, though. I am hard pressed to find any advatantages to it that one cannot find in better form with all the other attacks. After all, if, for instance, you want more reach, than it's better than Cryo Cross, but it costs almost the same, yet hits only 5 tiles to Cryo Cross' 12. Better go for Dark Vortex then, with 4 PsP more cost, it covers 9 tiles and can damage many more combinations of enemy formations. And if you want to go cheap, then Dark Vortex may be too expensive, but Cryo Cross costs only 1 PsP more and covers more than twice the area! Either way, there is always a better alternative, in my opinion.
Here is a challenge: can anyone come up with a very good reason or a good battlefield situation where Pyro Hail can be often and frequently used in prefernce to the other 3 attacks?
I really think that Pyro Hail is in a transient class of it's own: it's more advanced than the Elemental Breaths, but it's lower class than the other 3 elemental area attacks. The Heat equivalent would be Fire Gate, which has range exactly between Dark Vortex and Light Bomb.