It's not about them being similar or not, its about the fact you *can* even be one shot and having an ability on a 4 second cooldown that has the *potential* to oneshot.
They are
They're both instagibs usually with minimal opportunity to react and they both rely on questionable physics
The main difference is that one requires being close and putting in minimal effort to aim, while the other can be done at any range up to 20m with slightly more aim required. :^)
