I'm 1 kyu. I don't have any problem winning against two 6 kyus (I saw some experiments like that in the past.) There are simply too many things they overlook. And two 1 kyus (or a room of them) won't win against a 4 dan. We're playing different games.

What happens is that the weaker players become a little better at don't making reading mistakes and at finding possible moves. Unfortunately they don't get any better at evaluating moves and the unknown unknowns are still unknown. The better player finds moves that none of the weaker ones would think about or be able to explain.

I can imagine that the knowledge about the game of two 11 kyus have a smaller intersection than the ones of 6 kyus. This means they become much better together.

However two 1 kyu have about the same knowledge, so they could be at most 1 dan together, probably still 1 kyu.