If I have the overshield perk, I can't use the healing perk. In order for a Titan to survive a GG shot in Sunbreaker form, they need to be specced for max armor at the very least. I'm not sure if it requires overshield or solar defense armor. Until someone gets a group together to sit there and test it, players are going off game experience and there's a ton that can affect that. Lag being one of them.