You're confusing two different things. Lobbies have nothing to do with it, and nobody is asking for a single player game. Try to understand the basic argument before labeling it "crying"
The complaint is that these servers have several times the amount of players the most populated vanilla servers did, but the gameplay was not changed in any way to account for it. Things are overcrowded to the point of inability to do basic shit within the game. Areas that would be previously largely uninhabited are swarming with players every 100 yards, and the majority of quest targets in many areas have people camping their spawn like it was day one starter areas. When I was flying over shimmering flats at around 7est, half the mobs were dead and most of the others had players actively killing them.
Consider that these servers have the capacity of retail servers, but don't have cross realm stuff which acts as layering, don't have the majority of players in instances, and have zones that are a fraction the size of new zones.
Layering is supposed to be gone by phase 2, which is when most people will have hit 60, and things are going to be fucking absurd as you'll have thousands of people trying to cram into the small handful of relevant endgame zones.