Well personally for me I had good groups of peeps for sky and what not, so I can't attest to Kirin being difficult, (LONG ASS FIGHT) but never difficult. I think the truly hardest fight for me was back in FFXI and it was against Maat for my G5 as RDM.

I spent months prepping for that fight, even borrowing a friends Enfeebling torque, cause I was afraid my Spider Torque would not be enough. Having the right HQ food, having my testimony ready for when I was ready, all my gear sets, HQ elemental staves (though all I had at the time was Dark/Light for Cures/Sleep landing.) All my pieces for Enfeebling and Elemental spells, even for healing and enhancing just to have the max I possibly could achieve at the time. That fight was so prep intensive and going into and doing the fight it was as if the fight lasted for hours yet was over in the blink of an eye, especially when you lost.

I honestly would LOVE Maat/G5 type fights to make it into FFXIV:ARR. Would really prove you know your job well, and it was fun no matter how hard it was for me back on the RDM Maat fight (Went 2/23 on that fight, went basically 1/1 on the other jobs I got to 75.)