KA one shots all shinobi.
Give me a counter?
Well, it's possible the eye technique requires direct eye contact, similar to Tsukuyomi. It's also possible that Shinobi can "sense" when the attack is going to occur (Nagato was able to sense when Amaterasu was coming prior to Itachi using it), so that could give an opening to avoid the attack. When all else fails, I bet that certain Shinobi might be able to overcome the KA (perhaps a skilled Uchiha or a Jinchuuriki who's made friends with his Bijuu). I know Itachi planned to use KA on Sasuke, but there's no guarantee it'd actually work.
Look at it this way; Shisui attempted to use KA to prevent the Uchiha Massacre, and not only did he fail, but he was defeated and had his eye taken. So obviously it's not a free win... he even most likely had two chances at it, considering both his eyes are capable of using KA.
The rest of Danzou is pretty lackluster. Even with Izanagi spam, his own jutsu are pretty worthless... he just stands around making you wait 10 minutes to defeat him. A lot of upper S-class ninjas (everyone on the top 15-20 list) wouldn't have much of a problem. He honestly didn't even push Sasuke to the limit, it's just that Sasuke was still unlocking his powers and wasted a lot of chakra figuring out Danzou's abilities.