Which is why outlander is in play. The ability to pick fights with very nearly 100% impunity even if people know you are there is what is OP. Why engage someone geared to fight you? Just look at them, see their gear, and then move along.

Camo and hide both protect classes with them in similar ways, but even assassin hide has more restrictions than duo *and* if someone can see you, they can strike. Duo stops even that. Unless there is some hidden hard counter to duo (enemy muter?) that I'm not aware of, the issue with muters is really an issue with duo being too good, or the combo of duo + chamo being too good, not because you can be both at the same time, but because you can switch between when the situation warrants, giving you zero? enemies who can both see you and do something about it directly.