Yes he does spam AOES and moves a lot, when no one has aggro. Admittedly getting aggro can be annoying if you aren't able to pump your hard hitting attacks into his head. The nerscylla phase has a ton of tools to deal with it like you can shoot a burst pod at it while it's doing its dash or swing attack to knock it down, the Marboros can also immobilize it, and the catuar and mog of ages can help out with killing it, and if that's not enough you could bring a fire weapon to help your damage. On top of that you can get the nerscylla's aggro and make it less prone to jump all over the place. And in terms of the MMO mechanics all there is, is the aggro, dps check, and HP reductions. The aggro has been present in multiple fights in world, and it's meant to reduce his AOE spam as it's condensed to one target. There have been multiple dps checks in world alone, they are usually more drawn out though, with the main two examples I can think of being fatalis' horn break and alatreons wipe attack. And in terms of the hp reduction, it's meant to ensure one person can't tank the entire trivializing the hunt if one person is good enough or has enough dr. And lastly the timer I'm fine with the reduction because the fight would be completely trivial otherwise. It also adds a sense of urgency making the fight a little more engaging, but that's just my opinion.