If the life leach is that big, why not destroy the enemy citadel? This sounds if the game became cat+mouse.
With the current war ranking and citadel upgrades the game is almost certain over when Giants are entering the game. I really can not understand why a game would last 2 hours.
And if this is a balance problem then come here with numbers. Now you are just telling the balance needs to be changed and not how the numbers are causing problems will do no good. In this case:
HP of the used demigods + HP regenerations numbers
Damage done by the DM's
And yes if it turns out damage/s < hp/s then there could be a balance problem.