Btw, what happened in the anime is not cannon, most of it didnt happen in the manga. Deva path was on the defensive and was fleeing until he finally used Chibaku Tensei... he wasnt matchning 6 tails Naruto at all, he was pushed back.
Secondly, people are underestimating Itachi's chakra pool way too much.
You doubt that Itachi can use multiple high techniques several times back to back?
Itachi used all the following while he was DYING SICK, DYING SICK :
Multiple Genjutsu
Crow Bunshin
Tsukuyomi
Katon Fireball
Katon Fireball
Amaterasu
Amaterasu
Stopped Amaterasu's flames
Susano once
Susano second
Transfered an Amaterasu seal to Sasuke
All the bold ones mean these were Mangekyo techniques aka Very high chakra cost techniques.... he used all these while being sick, i'm sure he can use at least 2 of them in succession as he actually did 3 of them against Sasuke when perferming the Amaterasus and when stopping it's flames....
And you do realise that Nagato can,t spam Chibaku tensei and Shou Shinra Tensei..... he used these two moves and started having nosebleed and loosing chakra control, which cost him his lost against Naruto as Deva fell on his knees and couldnt keep up.
Also, Gaara didnt use the sand outside of Susano, he used the sand right under Madara's feet which is why he was able to get Madara out of his Susano... go look at it again... the sand from outside couldnt get in, Gaara himself mentionned it was MEANINGLESS to attack Susano's outside.
Gravity won't be able to pull Itachi from his Susano as there is no physical link, on top of that.... Itachi's has Yata's mirror.
And by the way... are seriously thinking Deva realm is immune to Genjutsu somehow??? He isnt... Nagato couldnt break the paths out of Genjutsu despite feeding them with constant chakra...
Deva path,, just like any other person who has encountered Itachi,,, will be fooled by Genjutsu.
Itachi wins this.... clearly. Deva realm is strong but it aint strong enough to take Itachi....