They were surprised because Sasuke didn't have the cursed seal anymore but managed to pull this of. It only later, thanks to Oro, was clear that it is Juugos chakra that Sasuke is able to channel.
But since it was known fact that Sasuke has powers over the cursed seal I would rather give more...
Yeah I agree with you. They don't see every aspect as we do. But I think actually after a good discussion/argue it can be proven that Sasuke wasn't so murderous bastard as Konoha sees him. As you already mentioned without him the alliance hadn't had this Hokage reinforcement.
But Sasuke did...
I have been reading this forum for a long time without commenting and the thing that I see is that many people don't realise that there are more people in the world of this manga than our usual ~20.
There have been thousands of Uchias and only 6 have awekened Mangekyo. Not much if you ask...
