As someone who was 340 for 4.2 abd 370 for 4.4 I'll tell you right now that nothing in Sigmascape or Hell's Lid/Fractal ever chunked my health to about 1/3 even with a cooldown, I actually need to plan my cooldowns for O11 on normal, people need to be coordinated in order to handle most of the mechanics in Alphascape otherwise you'll get one shot.
Arboretum also has some interesting mechanics with the sliding on the second boss and then having to protect the pooplet from AoEs otherwise you wipe.
The Mist Dragon is a fight that requires you to have enough situational awareness to avoid expanding AoEs based solely on where they'll originate from, you need to place other AoEs in a way that won't mess up your larty members and more importantly if you're hit by anything it's almost a guaranteed death, even as an i370 tank.

Compare this to Hell's Lid's bosses, which were mostly just smacking them and avoiding AoEs... same with Fractal HM and Swallow's Compass.

Is the content hard? Probably not, but it's certainly harder than what we've had before in this expansion.