Giant massing, or massing of any kind for that manner, just seems fundamentally wrong.
Unless the game has been imbalanced so that
1. Creating a horde of giants
2. Winning with the horde of giants
is a sure win, and that the process of
1 is inevitable, then there is a way to beat giant massers.
So we can either stop our enemy at
1 or
2, assuming the game is not imbalanced. I'll adress
2, just because
1 is pretty damn complex and is situation dependent.
What are giants? (and their weaknesses?)
Meat shields. Their attack isn't that great, in terms of actual damage. Correct me if I'm wrong, but to my knowledge it takes a fully grown giant two hits to take out one miner. That's pretty low, considering I just spent 1500 on the thing and that it takes up 7 population, and that the delay between their attacks is quite large.
Their strength comes from their massive health, and the fact that they can stun.
This means when people mass semi-strong units like the shinobi (you'd typically have about perhaps 15, on a good day), if you face a giant masser with 7 or so giants, that's almost half your army that will be stunned, and likely killed, as they try to escape, having only brought down 1 giant. Ooh, and look, he has another giant in the training que! And let's not forget that two shinobi take longer to train than one giant.
Fun.
So we have our problem there. When giants can stun, and are built up in their masses, their relatively tiny damage gets magnified and they become an almost unstoppable force.
Therefore, the solution to giants is to create ANOTHER unit that can take large amounts of damage, and is immune to stun!
But hang on a minute ...I swear we have that already ...wait, aren't they called ...giants?
"But does that mean we're just supposed to out-giant them? Isn't that a bit crude?"
Well if you thought I suggested outnumbering their giants, you're going about this the wrong way.
Ok, once again
a guy rushed me with EIGHT GIANTS!!!!
again, my army with ninjas spearton and swordwraths just get PWNED
Giants massers really really suck!!!!!!!!!!!!!!! OOOOPPPPPPP!!!!
Let's take the example above and say the enemy has eight giants. Nothing but eight giants.
If we had, say ..seven giants. We'd lose if we left it at that, of course. But my point is that having 1 or 2 giants slightly less than the enemy will not make you lose the game immediately. You have a window of opportunity, before your giants perish. What's important is what you do with this window.
So, how do we exploit 8 giants, standing in the same spot, for what will be a good few minutes? If only we had a unit that had a decent amount of splash damage.
Oh wait. It's called a wizard.
I don't think it'd be too difficult to force a win from here.