I know people are always going to get upset about the whole "Just dodge it" thing, but really I don't think it's bad design to have real one shots.
The biggest design issues are the context around the one shots, and what leads to something being "fine", or "unhealthy".
Three aspects I think the major issues boil down to, and that A-net should strive towards correcting, with a bit of forward thinking is an imbalance of:
A. How hard is it to land? - Does it have a tell? a long cast time? Is it hidden in stealth? What is the range? Is it a single hit? Did it have to be sufficiently set up? Or possibly channel that can be interrupted? I've always advocated for the need to read and anticipate your opponent, if there is no tell and no hand-crafted designed counter play, and you successfully avoid it; then B.
B. What are their follow up options? - Do they go back to being invis? Do they spam blocks and evades? Do they create distance? How long are these people reliably able to live after their significant whiff? Can they instantly heal to full from critical? If they can kill me in one shot, turnabout should be fair play. I should- BY DESIGN be able to reliably "punish" them, and them not just freely escape. If they can freely escape; Then C.
C. How frequently can this be done? - Is this on a long 2-3 min CD I win button? Was it a multifaceted combo that required a 30 second c/d to set up? Or can this all just be pulled off again in 10 seconds with out any risk thanks to "B"?
Maybe room for a 4th over encompassing category with "D. how many" one shot options like this can be done.
Either way there needs to be some sort of balance between this otherwise one shots become unhealthy. It's hard to say what exactly is fair and what isn't especially when trying to have a diverse cast. However, there needs to be some equality to ALL kits for those that have to much, and for those that have to little. There should be a standardized upper-limit and lower limit to what a build is capable of, and I'm certain there should be more than enough fair play between, so long as the limits are kept in mind by design. <- Watching patches since release I feel like this is not considered, and if it is, then A-net does a poor job of it or is narrow minded to context.
Now sure, one shots feels bad to less experienced players, and experts can get blind sided and frustrated, but for beginners once you overcome that curve it becomes second nature, and a vast majority of the attempts made on you are played around. And if more skilled players never got blind sided or put into a situation where they run out of options, we'd have a game of conquest where no one died, and that is even less healthy than a game where everyone's constantly dying.
Either way/tl;dr "just dodge it" is more or less valid, the issue I see is often what follows.