About Vine Ogres : I don't find them ultra-powerful, but
1/ They are an incredible bargain at 1 to 4 Ogres PER GEM ! Cite me anything even marginally useful costing that little... For example you can get 32 of them for the cost of those famous Drakes
2/ The whole Ogre Factory stuff is totally gamey. With say 10 natures/turn, every 2 turns you get an Ivy King (summoned by a previous IK with a Mace), all kings set to Ogre summoning, you get ridiculous masses of Ogres. Kind of same than clam-hoarding, gamey ... So it has to be addressed, the most obvious way being to prevent auto-summoning of IK so at least you've to devote some mage(s) to do the work !!