I'd have to ask to OP, what was your iLvl when you were doing this raid ? Did you have any Vulnerability debuff stacks on when you took the damage ? Were you full health ?

Because in my case, i did it as iLvl 458 WHM, and i got hit by this attack a couple times, but it never was an instant death, even with Vulnerability 1~2 ... The only time my team wiped on E7 was when we weren't able to kill the adds in time and the boss enraged.
So i am surprised that you were one shot by it.

Actually of all 4 new Eden raids, i think E7 has to be my favorite so far (with E8). It has a couple mechanics that are really cool in my opinion. On the other hand, i thought E5 was way too easy, and E6 too messy to understand what is going on.

Also, i personally don't think "normal difficulty" should equal "first try clear". I am happy to find a bit of challenge even in normal mode.

Another advice i can give you is to not try new raids with randos on the CF right after they came out. Most people don't know how they work yet. Your experience would be more fun if you party up with people from your FC, for instance.