If you think it means anything other than an attack readily capable of dropping you from full HP to zero, your definition is wrong anyway. The entire definition of a 1-shot is being straight up killed by an attack from full HP, something this game loves to do with a lot of its content in order to present "challenge" so it's not like the idea should be unfamiliar to anybody.I guess you just need to look up what a "one-shot mechanic" means. Here's a hint: it doesn't mean what you think it means.
If you're trying to say Vishap doesn't have numerous means of accomplishing this, you're also wrong.
I have never seen any non-tank survive a hit from Mistral Song in storymode Garuda, so even ruling out an unmitigated Aerial Blast, she certainly does have these. Wicked Wheel was also a common melee killer in Garuda EX before people started to overgear/Echo the fight and was a big part of the reason why ranged DPS became so prevalent in the fight and melees were left out in the cold.It actually does matter if it was designed that way. After all if it was designed to always one-shot you that would probably be the first thing to be nerfed (and already would be at that most likely.) But it isn't just designed to do a lot of damage. Similar to how some of Garuda's attacks are designed to do lots of damage, but aren't straight out one shot mechanics.
Not saying it is impossible to survive Mistral Song in storymode Garuda as a non-tank, but usually it's not going to happen, which in my book qualifies it as a potential 1-shot attack.
Another similar example: Batraal's pewpew laser in Dzemael Darkhold. Almost always, any non-tank that gets hit by this is going to die, period. If you try to pass off the attack as anything but a potential 1-shotter, you're not giving the correct impression of how important it is for it to be dodged.