explain please? pain may have the field advantage but they are more vulnerable than nagato, so it balances out either way.
besides, it's not like itachi (edo atleast) couldn't match 6 paths with 3-5 clones.
Itachi excels in 1 on 1 battles. Genjutsu (unless it travels through multiple bodies because of shared vision) can only be cast on one target at a time, and Pain's shared vision means only one path even has to look at him at a time.
Amaterasu doesn't help much, as Preta can likely absorb it, Deva can repel it, and Naraka can repair any bodies that go down.
Summons are a huge problem for Itachi, as he would have to expend a lot of chakra to take care of them permanently.
Susano'o is almost required in order to evade Deva, Summons, and Asura path, which means his chakra will be drained relatively quickly.
Tsukuyomi is far
far too risky.
Feints don't exactly work against 6+ fields of vision.
Katon Jutsus are absorbed, repelled, or repaired.
Itachi outclasses in speed, but again, the paths can be repaired, and a blitz won't work 6 times in a row before any counter can be implemented.
BUT
Nearly all of this is nullified against Nagato himself.
Genjutsu absolutely works just as well as against any other single opponent.
Amaterasu can immobilize, stall, or even kill Nagato.
Summons are dispelled instantly when Nagato is defeated, so as long as Itachi can take him down quickly, the summons won't be a problem.
Susano'o is only required against a single target, meaning it can be turned on and off when needed, and attacks will only come one at a time, meaning they could even be avoided if possible.
Tsukuyomi, like Genjutsu, is extremely effective against a single target, and there is no chance the chakra drain will be taken advantage of.
Feints are Itachi's specialty, and work extremely well against a single field of vision (assuming Summons aren't a priority).
Katon Jutsus can be absorbed, or repelled, but not repaired, and can act as distractions and feints against a single set of eyes.
Itachi still outclasses in speed, and only has to blitz or overcome Nagato once, rather than 6 times.