The main dent was 3rd hokage dying.
the 2nd dent would have been gaara attacking the village, but last i checked bijuu are much stronger than ninja.
So saying the shukaku would have destroyed lots doesnt really prove much, other than its stronger than ninja, which we all kind of already know...
Again, for the coup to be successful or damaging to Konoha you need the clan itself to be stronger than Konoha itself minus themselves.
Meaning they have to represent 50%+ of Konohas entire militaristic power, which would be retarded because then there would be no reason for the coup.
The reason they were going ahead with a coup was because they were being ostracised and being pushed down in power and rank, so if anything itd be the other way around.
Theyd kill quite a few Lead Ninja but they would have been dealt with very fast.
Itachi managed to kill the entire clan without amaterasu or susano'o (same as tobi)
so yeah, Itachi and Tobi are super geniuses, but they didn't even use their good techs (we saw no black fire in the clans area when sasuke was running through there, or burnt buildings, or smashed buildings, in fact everything looked intact.
It was a simple feat for Itachi and Madara even without using MS techs.
It seemed clearly like a sneak attack.. Something that the clan didn't had power of reaction..Not that matters because Itachi still would have killed them all even if they had time to react and prepare.