1st bolded part: do you have any proof that genjutsu would have been effective if nagato wasn't edo tenseid?? OBVIOUSLY NOT!!! OH WAIT!! I JUST REALIZED SOMETHING KOTO AMATSUKI WAS EFFECTIVE ON ITACHI WHO WAS A EDO TENSEI AND IT WORKED??? HOW IS THIS POSSIBLE OMGOMGOMG OMGOMGOGMOG wrong.... IT TOOK THE BEST GENJUTSU TO MAKE SOMEONE OF ITACHI'S CALIBER TO FALL INTO IT!! Same would have happened with Nagato (Jiraiya's frog genjutsu is no push-over technique).*Sighs*. U_U Would u please stop cursin and sayin "fanboy" That "sh!t is getting old. And what did i twist?
And Luckily Nagato was an Edo Tensei, so he was immune to Genjutsu. (except Kotoamatsukami). Because if Nagato wasen't an Edo Tensei, Itachi could've easily just pointed a finger at Nagato and immobilize him, placing him in a Genjutsu and that would've left Nagato open for an easy finish.
So as soon as Nagato prepares Chibaku Tensei, all Itachi has to do place a Genjutsu. Chibaku Tensei is not an instantaneous death. The victim will have plenty of time to think and elaborate, before he gets crushed. And Thats something Itachi does well.
And Genjutsu is Itachi's biggest factor and strength, while it's Nagato's weak point, weakness. (proved by jiraiya). So Nagato is easily open for a Genjutsu.
And Amaterasu is enough to destroy Chibaku Tensei.
As I have stated many times finger genjutsu is like a C-rank technique if compared to Frog Song which can be considered a A-Rank and Tsukuyomi and koto amatsuki as a S-Rank.
Summary: If Itachi was able to fall in genjutsu (Koto Amatsuki) then why Nagato isn't??. So Nagato is as same as vulnerable to genjutsu as itachi during his Edo tensei version.
Bolded part 2: Once again WRONG!! Pain was caught in genjutsu CORRECT. BUT HE NEVER STATED THAT GENJUTSU WAS HIS WEAKNESS. EVEN MORE I HAVE MY OWN WAYS TO SAY THAT HE GOT GENJUTSU PROWESS, for example we know that Rinnegan gives ying release which according to 3rd mizukage, you are much likely a natural genjutsu pontential user. We also have seen the mind block made by pain on his subordinates minds too.
Summary: By having Ying Release, able to put mind blocks on his subordinates we know that he can play mind tricks and games and EVEN PROTECT HIMSELF TOO.
Bolded part 3: With all due respect, but this HAS NO LOGIC. First of all we know that amaterasu does NOT incinerates INSTANTLY, tell me how long raikage was able to have amaterasu on his arm and everything that happened and occured and amaterasu hasn't burnt him yet? Second to this, If Itachi happened to throw amaterasu at the chibaku tensei planet, and as we already know it won't burn instantly, have you realized that itachi would not be going straight to a big rocky planet, BUT TO A BIG ROCKY PLANET COVERED IN THOSE BLACK FLAMES?? WHICH IS WORST THAN BEFORE.
Summary: Amaterasu does not incinerates instantly, if Itachi were to throw amaterasu at Chibaku Tensei it would make things worst by setting on fire his own tomb.