Recorded this a long time ago but never got around to uploading it. Here's Leviathan EX fight with me playing WHM. I've also tanked it and done it on scholar if anyone is interested I can try to do it again on them, but I'll warn you being tank on the fight is kinda boring to watch there's not a whole lot going on.
I find interesting how things can seem so hard in the game but then once you figure out the gimmicks they become incredibly simple to do. When Leviathan first came out I thought it was hard to heal because I had no idea what was going on at all. Now when I play it on scholar I am pretty much just doing damage the entire time and hardly healing.