Hmm... that makes me think of Dominions, because in Dominions, you definitely need different types of units (or at least strategies) to defeat the different nations. For instance, to defeat Abysia, you will need a lot of fire resistance spells and items just to counteract their deadly radiant heat. In SE5, last I'd heard, we'll be able to make up our own damage types and resistance types, so you could for instance give the Eee different components than everyone else (to reflect the fact that they're energy beings) which are particularly vulnerable to shield depleters. Actually, this is already being done in a somewhat different way in SE4 by Fyron in the Adamant Mod; the Eee, being an energy race, will get components with half the normal hitpoints, but extra phased shield generation, so they literally will be vulnerable to shield depleters!
