They are referring to LazyPeon times, at one point his followers bolstered server population to the point that the Devs decided to up the player limit to where it stands now - 3500. It didn't last long though. Sure, there's people that just come check a game out and all, but a bigger problem is that this implementation of WAR has a very unforgiving environment for a newb to learn and develop his toon. It was at this time that I and others started suggesting to the Devs that reinstating a mid tier system of some sort to isolate lower level players from BIS RR80s might help to keep newbs interested. Nothing was changed. Not that this is the cause, but within a month regular population dropped from 1500-2400 at peaks back down to around 1000.
I remember a youtube event with some gamer and Max, and others from the Dev team shortly after the surge ended. During it the devs had looked at character creation and development over time. What they found was that a great many had created new toons but a large percentage had given up before hitting level 20. To me the message was clear, the grind of playing this game was just too much to keep the average player's interest.
As a player on this server since T1 was the only zone, there have been many months where average population (on a weekend at least) easily hit 1500. But as mentioned in other posts here, things like the GCD change, lack of balance changes, lack of bug fixes (Mara pull, etc) and now the complete upheaval of what was by way of the ability system implementation really have long time players (are there really any left besides me) wondering about their loyalty to the project.
I found a Q&A. You can see Peak Weekly population at: 8:59
https://www.youtube.com/watch?v=mELLo7L0el4
And this Q&A. Overall class creation percentages and population RR level comparison discussion starts at 11:20
https://www.youtube.com/watch?v=OBZP_BtrA_U
