I agree with the fact that the sorcerrers are pretty strong and might need some nerfs, although the fact of them defending their building is not bad.
I disagree with the idea to make them just like the way Saruman is used for Isengard, but when their building reaches lvl 3 there should be a mage on a balcony protecting the building, just like some buildings have arrows to shoot at enemies, why not to let the building have a mage protecting it, using the standard abilities of the mages but nerfed.
Thus the uniqueness of Isengard with saruman is still there and the sorcerers are used in a different way defending their building.
May I add that I utterly hate the sorcerers as they are disturbingly opposite with the Tolkien world's way of magic, which was used only by several creatures of certain power and not by any of the races of Middle- Earth, with a wierd exception for the elves (thanks to their rings, which were made by the power of Sauron's magic).
But this is an entirely different matter