I must be getting old

[Omni-Odin]

So here's the deal. After going all the way through Lightning Returns, I am absolutely getting my arse kicked by the final boss. I wan't able to beat aeronite or Ereshkigal and the Earth Eater Last One can suck it. I figured, "Hey, those are optional bosses. I'll do another play through after I beat the inevitably easier final boss to get better gear and stats. Oh crap, I can't do a lick of damage."

So, maybe I'm just getting older, and can't adapt to this (difficult to me) battle system, but I find this to be the hardest final boss in a Final Fantasy I've ever walked into as close to fully garbed as possible. (No Ultimatum garb or Falcon Charm) So, here's my question. Which of these games that I consider to be main series had the hardest final boss for you.

EDIT: Finally beat him. My God. I was thinking about throwing the controller if he mutated into another form.