Bill Zebub
“It’s probably Matt Mercer’s fault.”
So the question then is how many orcs before they get advantage?
I think it's a realism vs. narrativist (rule of cool) sort of thing, and depends on which way you lean.
I'm definitely in the latter camp. It should actually be easier to sneak past 100 orcs than just one, because if one orc sees you there are lots of different cool stories that can still happen. If 100 orcs see you it's still possible to have a good story, but much more likely that you just die.