As of now, the only dlc op that could've worked as 3 armor is funny enough Blackbeard since he is effective a shield operator. He basically has a shield that can be destroyed in exchange for being able to use his primary and have the shield equipped when rappelling.

Another thing that makes 3 armor attackers difficult is distance. Attackers have to travel to the objective site so having a slow 3 armor makes that process worse. For defenders though, you can justify 3 armors by having their primary role as anchors who don't need to move much so it works out. A common complaint for Fuze players is how Sledge and Ash mains always run ahead and destroy every window before they can deploy his cluster charges.