I'm not counting anything that can kill a player, I'm counting every single attack that can kill a player.
Faerlina's poison volley is a oneshot mechanic.
Patchwerk's cleave is a oneshot mechanic.
Grobbulus' slime spray is a oneshot mechanic.
Sure but you can say exactly that for GW2 too. People think GL has lots of one-shot mechanics while he only has 1 in phase1. Mage crusher has a cleave OHK but simply strafing sideways will negate it completely (competent groups can even make bosses like this face one way all the time). But even though it's really easy to avoid, it's still a OHK mechanic.
Let's flip it to GW2 and throw out a random dungeon and we'll figure out for each path howmany fights have one-shot mechanics. If you're not going to count "cleave" as a one-shot it's basically 0.
The difference is you're so used to automatically negating the mechanics by attacking behind the boss and stacking that you completely forget that the mechanic is still there.
It's also the first (and easiest) raid of that content so it's normal that there are hardly any oneshot mechanics.