If your sovereign has 20 essence with a 500% bonus from 10 Temples (not hard on a large map) he has 120 essence to work with for most things. When you cast Imbue champion it takes 3 essence from the base 20, not from the boosted 120. So one cast would leave you with a base of 17 and a boosted total of 102. The champion would have 3 base essence and a boosted total of 18.
Although one game I played I had somewhere around 3,200% bonus to essence so 3 essence became 96.... I don't know what I had between techs, shards, and temples, but I controlled about half of a large map with enough city centers an average of 8 squares apart.
A lot of these misunderstandings come from players who haven't spent any time learning various strategies, and think in terms of "one right way" and who are going up against a blind deaf retarded AI with one hand and both legs tied behind its back. If you don't imbue your heroes, your sovreign ends up with an enormous mana pool. The fact that most tactical spells worth using in late game cost 15 mana and have a roughly 2% chance of doing anything at all... means you need to have a LOT of mana, and focus most of your level points on intelligence in order to keep up with the escalating defense and health stats of an enemy army or random monster spawn. If you DON'T have 100 mana and you run into an "elemental lord" in the woods, you'd better have a couple of military units that cost over 2K gildar already built, or that thing is going to march across your kingdom razing cities, and single-handedly wipe out half the map. In a multiplayer game that goes past 200 turns, this will be a major issue. People who DO imbue their heroes will need to spend most of their level up points on essence, since it costs an entire level worth of character points per hero you imbue just to keep an even keel on your sovreign. This combined with multiple magic-using offspring CAN create quite an army of summoned critters, but keep in mind also that mana takes a long time to regen even if you have all the bonuses, so there is an even greater time restriction on summoned armies than on paid-for ones. Roll those THREE different kinds of strategies into one, imbue a few heroes, stock up on sovreign's INT, lead armies of combined spell-casters and military stacks and summoned monsters into battle, and you stand a pretty good chance of facerolling anyone who super-specialized in one of the other three options. Yet another option is to have your sovreign and one or two others just go around casting hexes on enemy cities, while boosting the hell out of your diplomacy and making a ton of Gildar by selling all your materials, and causing the AI to fight with itself so you don't have to actually get involved and lose anything. This is the alliances strategy, and requires an ENORMUOS amount of mana concentrated into only a couple of units that can run really far every turn. Sometimes the AI will have so many gigantic units stacked in a city at the same time, you just can't take it, that's when the hex strategy works best.
Another strategy is the cold-war, where you pressure your borders into the enemy that you are paying to be friendly, and slowly crawl across their resources until you have dominated their economy. Then use all that money you made to pay someone else to declare war to deplete their units down to where their economy levels out, THEN take their overly-fortified cities with a surprise attack from behind.
For some of these strategies, it would be nice if the AI gave a crap about "honor" like it does in Civ games, and SMAC, and GalCiv and so on. That's pretty complex coding though so I understand why it hasn't been added yet.
