Here are several solutions, to somewhat nerf, Giant massing.
Solution 1:
Incrementally increase the price of giants with a reset. That means, the first giant is 1500, the second giant is 1600, the third giant is 1700. If you have 3 giants, and two die, then the next giant you build, will once again, be 1600. The prices are just an example.
Solution 2:
Incrementally increase the price of giants without a reset. That means, the first giant is 1500, the second giant is 1600, the third giant is 1700. If you have 3 giants, and two die, then the next giant you build, will be 1800. There of course would be a maximum price, in this example, it would be 2500. That means, the giants are worth more, so don't let them die.
Solution 3:
Remove the third tier of giants. Very simple.
Solution 4:
Increase the price per level. A normal, level 1 giant, is 1500 - 0 - 7. A giant, after the first upgrade, is 1750 - 75 - 8. A giant, after the third upgrade, is 2000 - 150 - 9.
Solution 5:
Decrease the effects of the tiers. Miami has suggested that the maximum giant has 70% more health, and I believe he also has around 10% more damage than a standard giant. Make it, so the maximum giant only has 40% more health and keep the damage. Making them more of a support & tank unit, rather than the main army.
Solution 6:
Nerf the numbers! Do the opposite of Pack Mentality. If you have two giants, then their health & attack are both reduced by 5%. If you have three, then it's 10%. Four is 15%. Five is 20%.
Solution 7:
Make the ghost giant, either stay at level 1, or a maximum of level 2.
Solution 8:
Drastically increase the price of the tier upgrades.
All the numbers in here are only examples and can change.
These solutions are also only suggestions, parts of them can change.
I like solutions 1,4, & 7.