I tend to see duos in my games, others games, on stream, etc, usually not do so well.
You would think having that communication element, and assume they know the others playstyle a bit, they would play better than 2 strangers but...
It's a stereotype that duos do back because with all stereotypes, it came from somewhere, and it tends to at least have some truth to it.
When I see a duo go in different lanes, 1, they rarely say they are a duo, and 2, they do fine. When I see people try to force their way into bot together, it tends to disrupt champ select because they may not be the only ones wanting those positions, and tend to not budge on going them together and will complain if they don't duo in the same lane.
I've seen it the above way more often than I have not.