Nice but, no.
Using ST during CT would be pretty pointless. He'd be blowing away the rocks that are being pulled by CT, effectively giving ITachi more wiggle room. Also, Yata mirror is said to be invincible and all CT does is crush. It's unlikely it would crush through yata, especially since the kyuubi wasn't crushed by it.
Also, Nagato doesn't make unnessarily large CT's. He only makes them big enough to trap his opponent, else it takes too much chakra. If the CT is small enough, itachi may find a way to break out, or he could probably destroy the core on his own. Nothing says he actually needed Bee and naruto's help against the core, it was just the best strategy to use as it was the most likely one to work. Why use your most powerful attack, alone, and potentially fail, when you could use 3 very powerful attacks and most likely succeed?
There's also itachi's high movement speed, and nagato's lack of mobility. Itachi's shown the capability of bypassing his linked vision through use of his pin point shuriken skills, even around blind spots. He's even shown that he's able to take down the summonings using amaterasu. There's a 5 second interval between S/t, but there's none between Ama. If he blows away the first, itachi can already be using another.
Anyway... Nagato wins this fight, but not how you stated, he just has too many different abilities to properly contend with. CT isn't really a 1 shot move, it's more of a trap(sort of like izanami being a trap). If the opponent can get out, then the fight resumes. Therefore, nagato can't 1 shot itachi, nor does this fight ever end quick.
Rockets? - Susano'o
Summonings? - amaterasu
Human path? - Kage bushin feints (which he's able to do in mid fight, see itachi vs sasuke)
ST - Well, he gets blown away there, he doesn't have any counter to that.
BT - Ribcage susano'o to block the follow up attack
CT - Susano'o
All in all, itachi needs to use too many MS moves to contend, he'd die from exhaustion/blindness