I play on a Japanese server, but due to my work hours I rarely catch the crowd in raids except weekends. Server been mostly quiet during my weekday login time. As far compromise between super hard and somewhat hard content (for more causal raider), I would think the Ex Primals are the "somewhat hard content" (some or you will disagree with me), while Alexander Savage and Bahamut are the super hard things for the really hard content.
The Hard/Ex Primals do take practice. I guess Japanese players handle pugs quite well (it was the same way in FFXI), and are welcoming and patient in practice runs with runs dedicated for practice with instruction macros. At the same time, there are generally clear 3-strike-and-out as an unwritten rule for non-practice or duty/content finder extreme runs. You rarely see rage quits or deliberate trolling behaviour; humorously I have seen GUI (gaming under alcohol influence) a few times >_>. It was only like 3 weeks ago I cleared Ex Sephirot, and that was with a pug team. Generally, the more causal folks tend to be quite averaged out, and team work been pretty predictable with low variance (again it was like that in FFXI...). I do not know the situation in NA/EU servers with practice runs, but friends in NA servers do appear to struggle with pug. I am not familiar with the situation in Alexander Savage as I have never done one.
To be fair, I do really hate those instant-kill mechanics that are quite prevalent in Ex Primals. The original Ex/Hard Titan and the recent Ex Sephirot, the margin of error for DPS check is quite thin. Having one guy get instant killed and out of battlefield, you are pretty much screwed. At the same time, despite the notoriety of Titan, I will think Extreme Thordan is the hardest Ex to learn fully as it is only the Ex that the moves don't cycle.
Amanada (Cerberus-Retired) (aka MaiNoKen/Steven)
-- Thank you for the fun times in Vana'diel
Art for the sake of art itself is an idle sentence.
Art for the sake of truth, for the sake of what is
beautiful and good â€” that is the creed I seek.
- George Sand
A designer knows he has achieved perfection,
not when there is nothing left to add,
but when there is nothing left to take away.
- Antoine de Saint-ExupÃ©ry