Itachi will have a hard time fighting against pain. Amaterasu gets absorbed and tsukiyomi only works at one target at a time. Pain has way more win coins. Itachi healthy or not also is on timer with ms techniques.
Also don't know where you're getting Tsukuyomi only working on one target a time. Kakashi's basic sharingan genjutsu worked on 2 Anbu ninjas with one glare
And Itachi has far superior genjutsu than Kakashi with 3T alone let alone MS...
Itachi also put thousands of Aburame clan insects who were looking at him in a Tsukuyomi.
So Tsukuyomi is confirmed to work on multiple targets, thousands if the target is small enough.
Rest is fair. Itachi's biggest problem is CT activation and his own stamina