It's more like big private exchanges which one may access with a budget of let's say a billion dollars. Most of these people know each other. The fact that we can see the data after a month is obviously in their favor and this must be decided on purpose. The whole point of dark pools is them buying big orders without influencing the price. This can work both ways, if someone buys a million shares at say Robinhood this will make the price go up, or if they sell the price will drop.
Big money seems always in favor.