taking into consideration that in Elemental we will be able to create our own armies from the ground up, i can see these armies broken into three varients. now i'm not talking about whether these armies levels of balance between troop types but rather the overall tactical style of these armies.
I'll, more or less, break these into three types: the Elites, the Versatiles, and the Fodder. To help in illustrating my point i'll use the Starcraft's most basic units (the Protoss Zealot, the Terran Marine, and the Zergling) as examples
1.) Protoss Zealot (AKA Elite): Attack: 16 Hitpoints: 80 (plus 40 for plasma shield) Cost: 200 minerals (i think)
2.) Terran Marine (the versatile): Attack: 9(ranged) Hitpoints: 40 Cost: 100 minerals
3.) Zergling: Attack: 5 Hitpoints 35 Cost: 100 minerals (for two)
Naturally in a one on one fight (on open ground), the Zealot would easily defeat either the Marine and Zergling, while the Marine (taking his ranged attack into consideration) would suffer some damage from the Zergling before killing it.
Now lets say you have 1,000 minerals. You would gain either 5 Zealots, 10 Marines or 20 Zerglings. the Zealots as we know are tough and difficult to kill but sadly being an Elite force also means you wont have alot of them to spare, so using trickery and well planned manuevers to insure their survival rate. Marines, while not as effective as the Zealot on their own, you get more of them out on the field and, if you consintrate their fire, you could pin down a 5 man squad of Zealots and be on even footing with them. Zergling....what's there to talk about? their cheap, expendable and there's always a lot of them around. the only true power behind the Zergling is in the fact since you can build (four times more than Zealots and twice as many as the Marines) then the best tactic for them is to simply overwhelm the enemy with massive numbers.
The point is that, depending on your play style, your armies will either consist of Elite forces, highly flexible Versatile forces, a whole lot of Fodder or maybe even a combination of two or all three.