I dunno... As someone who knows their own limits and doesn't touch ex/savage/unreal at all, maybe I shouldn't say anything, but...

From what I've seen, we normally start seeing groups clear these fights in a few days, to at most a few weeks. Now consider FF Eleven,
where there were a couple of bosses that went unbeaten for five to six YEARS. That's the kind of thing that crosses my mind when I
think of 'ultimate difficulty level.'