They don't get one shot by shot. A good shotgun will do around 80%. Blink makes them a harder target, though it's also hard for them to hit you if you can blink towards them.
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If they have any bit of damage on them a shotgun will one shot. The majority of the time I'll use arcblade to run away, I mean what kind of super is that? In trials I'll activate it to scare the enemy team and get te revive. I'll admit against a bad team arc blade is god like. Any decent team will team shot you and destroy you.
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This, the only time I get kills with my arc blade is against a bad team or I use it to shut down selfres players. I have had my fair share of clutch moments with it but its mostly the other teams fault, arc blade is only good when your teammates have their attention or when you want to revive your teammates. Vanish allows you to flank a little easily but still doesn't bring it close to gunslinger.