One of the difference between a 1000 people server and constant immigrant/returning player adding to the population, and a 400 people population that's mostly stagnant, is that on 400 people server, everyone knows people on a higher degree. If you just met a player that came from Siren 2 days ago on Asura, you simply aren't going to know that person as well as someone that you've been playing with for 8 years. So while Asura is a bigger server with more people, it doesn't quite function the same as 400 people server because 70% of population on that bigger server are either new, returning player, or immigrants.