That's pretty much the problem. Warfare creates extremely powerful units fairly quickly if you focus on it, which is why Vigilant Minion armies aren't invincible, they simply can't take on powerful units. Vigilant Minions are viable as a rush strategy, not in the long-term.
Perhaps I should say, Vigilant Minions can't take on powerful units but they'll always butcher the AI.
If this was a MP thread, or if MP was even relevant at this point, I'd agree.
But it's not, and it isn't. "Butchering the AI" is exactly what the problem is, because of underlying balance issues with the unit itself. Since they're the only opponent we have, a sure fire way to butcher them is a problem. Elemental is a SP game until the MP is active, as far as I'm concerned.
As for rush vs. long term strategy, again, you ignore resources completely while making the warfare argument. Or do you have all the metal, material and crystals, research and economy by turn 100 to create 9x9 units of decked out Shock Troopers? THAT's luck. VM's are an imbued champion and 5 mana.
But let me offer some suggestions instead of just disagreeing with you.
-A cap on the total # of a summoned unit allowed.
-Arcane Doom costing all the VM's action points per round.
-Moving the VM to a higher spell level.
-Increasing the cost of their summon.
-Increasing the mana point cost of Arcane Doom.
-Removing true damage from the attack.
-Reducing the damage of the attack while keeping true damage.
It's all a balance issue right now, numbers vs. when they're introduced, and some unbalanced thinking in the way summons work. But it IS out of whack, and it IS by far one of the most useful units in the game, at perhaps the cheapest cost and easiest access.
(I play medium maps, maybe that helps me)
That has a lot to do with it.
I usually have won by turn 50
Then you're playing a short game. Of course you don't need more than 2 minions, the AI never built up to the point where you'd need more than that.