Yup the last boss is especially troublesome. I have pretty much decided that Helya is the hardest boss for my x5 hunter team. There is so much AoE, and the encounter cannot be nuked very easily due to the different phases and non optional waiting on boss to appear.

I've given it a few tries on just +1/2, but I've always wiped on the last boss. (Up to last boss it's a godlike timer) To beat it as x5 hunters you probably need to beat her before she submerges the first time in p2. With x5 hunters and heroism it's possible, which is why I've always rage quit after the first wipe. I was so damn close once. The dps isn't really the problem, rather it's characters who start dying... If I had legendary helm on all chars it would make the difference

Anyway nice work!