It's super simple- Wingman is immune to all debuffs. He still has 100 HP and can be hit by mollies, but Viper's post-plant revolves around Decay and Weakness to shred the health before the venom finishes them.
Enter Wingman on defuse. Viper's venom does very little damage without weakness, therefore Wingman tanks the damage and defuses at least half if not complete. Meanwhile, Viper's smoke blocks LOS to the critter and Gekko can see where the lineups come from. Once Viper's out of toxins, Gekko gets defuse off with time to spare. Even in a 1v1, as long as Gekko stays alive, Viper is screwed.