I've been gunned down in arc blade just as fast as when it is not active. If there is a damage reduction, it is far less than what fist of havoc and the warlocks nova bomb have. The Titan and warlock both become invincible when activating there supers. Hunters get 1 shot in both animations when activating arc blade as well as golden gun. If you head shot a Titan with a sniper in fist if havoc, they live. Check my xbone clips for proof...