[militarist]

I think cold blast is very underestimated because of it's short range. But several water mages , properly positioned spamming cold blasts on enemies whom you allowed to come closer instead of wasting all your fatigue on cold bolts or sailor's deaths, feel quite safe and are very devastating. And you get this spell very, very early. Just put your mages not behind archers, but between archers and heavy protected guys.
I use sailor's death only when the enemy has more ranged power, and i attack. In this case you just can't use blast. Theoretically sailor's death should be effective against high-protected units. it is, at least better then clot bolts. But still worse then cold blasts, even with heavy protected ones. If you can win the placement game, of course. And some risk is always involved.