I know this is one in a sea of posts suggesting ways to change essence, but I don't think I've seen this particular idea yet, so. . .

Essence should be the binary ability to utilize magic in the world.  It should be used to unlock the magical potential of heroes and shards.

Heroes with their magical abilities unlocked should have spellcasting ability then determined by their intelligence and wisdom alone. If a hero dies, the essence returns to the channeler, so a channeler's total essence remains the same, it's just a question of how it's distributed.

Shards should require essence to control.  If a shard is destroyed or control wrested to a new channeler, the essence returns to the channeler. On large maps, you probably wouldn't have enough essence to control a large percentage of the available shards until you had children with essence to help out.

A channeler's essence score should be used to determine how many magical heroes and elemental shards he or she can unlock.  A channeler's children should be born with essence (or perhaps a chance that they will be born with it, using the existing ways of deciding heredity).

Channelers who don't utilize their essence for shards or heroes should be more personally powerful, with bonuses to mana regeneration, spell learning, and combat prowess. Perhaps you start with all those essence bonuses, and each time you activate a shard or imbue a hero, you have to chose what portion of your essential powers to surrender.

I don't think essence should have anything to do with reviving the land.  That should remain in the realm of ordinary magic.