TsukuyomiKakashi

I honestly believe Itachi is a overrated character. If it weren't for his mangekyo( Or however you wanna spell it ) sharingan, he'd be dead 30 times over by now. He always ends up using that. Hell, he had to use it against Kakashi/Asuma/Kurenai when he is supposed to be levels beyond them strength wise. If he didn't retreat, Gai probably would have whooped him in episode 84/85( or whichever, I forget which it was ). Plus, he had to resort to Mangekyo to beat a very weakened Kakashi as well. So I really don't see why he is praised as so strong, cause if you where to take his Mangekyo away, he'd be dead now.

KosherKrackers

Could say that for a lot of characters: that they have one specific strength.

Take away Gai or Lee's brute strength and they've got nothing, take away Orochimaru's ability to change bodies and he'd have been dead quite a few times, take away Deidara's clay and he'd have been killed several times over, take away Sasori's puppets and he'd have been killed a LOT easier...

The thing about Itachi is that his unique strength is a hell of a lot more powerful than any of theirs.

TsukuyomiKakashi

Gai and Lee resort to physical training, not some mystical eye technique. Orochimaru has a ton of abilitys other then change bodys, I'm sure he can go without. Deidara is a good example for this too, as is Sasori. Seems like all of Akatsuki relys on one think really lol.

Sin

If they had none of that they would train on something they did have instead. They may not be as good a ninja but they would still be good.