Itachi's hardcore fans never cease to amaze me, but let's get this straight.
Yata mirror is pretty featless so I would hardly call it an invincible weapon, but even if we go by that, there are a few things that you need to keep in mind:
1) It hasn't 100% been proven to be able to protect Itachi from all directions and it got no answers against underground attacks.
2) Itachi has to use Susanoo in order to have access to it which would make him go blind pretty quickly or run out of chakra eventually if we're talking about "EMS Itachi" who still has low chakra reserves compared to Hashirama who literally can fight for 24 hours straight without running out of it.
I don't get the totsuka blade part, he doesn't need a counter to it at all, it will never touch him. This isn't your typical run of the mill ninja.
I would recommend you to re-read the last few chapters of the manga then because you clearly don't understand how someone can unlock the Rinnegan. Indra's reincarnations (Like Sasuke and Madara) are the only ones that have the potential to unlock it, Itachi's eyes had nothing to do with it.
Sasuke's rinnegan is special. Itachi wouldn't ever dream of getting his hands on it let alone handle its immense power.
Said novice can kill Itachi easily and has long surpassed him. Yeah, hax abilities, it's not like Itachi just so happened to have two spiritual weapons that came out of nowhere as well as a seriously random genjutsu. These are totally not hax abilities. Sure.
Well, I'm sorry to break it to you, but being a genius doesn't make controlling the rinnegan any easier. If someone that had half of their body made out of Hashi's cells could only handle one, then what can someone with low chakra reserves even be able to do?