Itachi has always had his time to shine.
Ever since he appeared in the series he has shined and people have regarded him as the strongest.
this is exactly the reason why he is SO OVERRATED.... since he's been first introduced everyone was like OMG Tsukuyomi is so OMG...... After that came Naruto, Kakashi, Sakura, Chiyo agaisn't him once again he showed something new finger genjutsu........ Then Sasuke vs Itachi (1)= OMG amaterasu is SO AMAZING........ After that OMG Susanoo he was able to stop kirin, orochimaru, BUT WAIT SASUKE WON THAT BATTLE...... But we all know that Itachi let Sasuke win this one....... AND MOST RECENTLY OMG KOTO AMATSUKI THE BEST GENJUTSU EVER!!~Has he ever been downgraded?? DEFINITELY NOT.....
As for Nagato..... He was first introduced in fight agaisn't Jiraiya...... OMG 3 on 1 that can suck chakra, take souls out and summon alot!..... WAIT
(TOAD GENJUTSU) First 3 pains= OWNED...... Then those 3 were revived and asura path practically DESTROYED JIRAIYA....... did pain shined?? DEFINITELY NO!!!!!!!! Because it was never stated that he was weak agaisn't genjutsu, he simply didn't expect one of THAT LEVEL coming from Jiraiya WHO NEVER USES GENJUTSU........................ Then later PAIN LITERARILY DESTROYED KONOHA (The supposedly "Strongest" Village) and owned it pretty badly.... But then Naruto came fresh in Sage Mode with 2 Battery Power recharges waiting for him and with deva path stripped from his powers.... And while deva was without his powers, Naruto destroyed 4 bodies (BUT NOONE EVER TOOK IN COUNT THAT IF DEVA HAD HIS POWERS THOSE 4 BODIES WOULD STILL BE AROUND) Then after that Pain had Naruto with his hands stabbed in the ground ready to be captured, but Hinata came out of nowhere made naruto go nine tails AND EVEN THEN Pain still fought nail to nail agaisn't the kyuubi..... Then he fought agaisn't Naruto ONCE AGAIN, and finally lost...
AND FEW PEOPLE ACKNOWLEDGE THIS AS A WIN FOR PAIN AFTER ALL THAT BATTLE AGAISN'T MORE THAN HUNDREDS OF KONOHA shinobis, and Naruto with SAGE MODE (3 times) and a kyuubi on his rampage.....
and in the most recent Nagato couldn't shine because it was 3v1
so nagato has not really ever shined..... But Itachi has
Compare both of this character situations and you will notice the difference