So simply because Itachi countered an attack in Mid air once, This makes all similar arugments flawed?.
I simply said it would leave him Open to an attack, If he could counter (depend on what kabuto decided to attack with) it Open for speculation.
Susanoo's arm is a blunt force, It's not exactly made for precise cutting.
In terms of Cutting kidomaru's webs, Nejis precise chakra strikes > Susanoo's Arm.
Neji using chakra to cut them removes the webs from actually touching neji thus prevented the webs from wrapping around his arms/hands. So neji wasn't physically touching the webs in order to cut them.
With this he could most likely cut the webs without to much trouble, But i can bring in the question on how fast can Susanoo swing that sword around. Could it swing fast enough to cut a volly of webs like neji failed to do.