I can to a point speak to this: I have characters on many worlds, in both data centers. The legacy worlds I am on are insanely densely populated still. The high load non-legacy are also heavily populated still, but they aren't heavily populated in the low level fate areas anymore. Low level dungeons are always well queued, but Mid level dungeons have few people. High story dungeons are always full. There seems to be a lull in the 35-44 range right now, though there are always people in titan (SM) queue.
Many of the newer worlds however appear to have severely low population density across the board, and it only got worse after free transfers.
I can only speculate without good numbers, but my guess is that many of these worlds only saw as high a density as they did because of story only solo'ers, and people who got separated from friends. Those latter gave up, or transferred last week, the former are either working their way through still, or gone, leaving some worlds in a bit of lurch.
The question is: will SE end up merging some of those worlds back in, or will the new joins make up for the lack soon resulting in a fresh spike. To a point I think that depends on how SE is managing new character creations on new accounts, i.e. are they encouraging specific worlds, or is it still likely to be a skewed population density?
But to the point: anybody who is only on one world, not to mention a specific timeframe, has a uniquely skewed perspective. Each world environment can feel very different right now, JP and NA are different, Legacy vs Non-Legacy are different. High density overfull, vs the emergency new worlds created for overflow. They all have very different feel to them right now. Which is why I try not to comment on this particular subject yet. Even though I have a wider swath of experience, I am not on (and never can be) all 60 at the same time, much less throughout the day.
On your server. Again, I am pointing that on other servers this is not always true. On one of my JP server level 20 fates are still a constant zerg fest to avoid. Over on another JP server I was on (just transfered off) the level 20 fates I had to try and solo with my chocobo if I tried them.
I find that there are roughly as many <30 in world as 44-50. So I am pointing out population density and new character creation differs from world to world.
Think about it like this, if the first million subscribers in the first month, distributed unevenly, but with overflow still resulted in a large number of new players in most worlds, then with an additional 500K this past month, (assuming at leas 90% of them are new not extra) the distribution is either going to be similar, or more distributed. That is there are still a lot of new people, but either a) you won't see as many because there are fewer then the first month, or b) you won't see as many on many servers because they are more concentrated on specific worlds.
Statistically it is most likely to be somewhere in between the two, but again without raw numbers I hesitate to speak much.
Again, I am saying every world is different. I am not, and have never been, on Shiva. But to my recollection it also has never ever been one of the highly populated worlds either, not even during the peak time all worlds were overloaded. My guess is whatever "draw" there is to specific worlds, has never drawn people to Shiva, and with the lower percentage of the 500K distribution, that means that smaller percentage wasn't really enough to cause an influx to your world.
It is about distribution patterns. Since I haven't seen an official one I can only guess based on previous feedback and my own in-world experience.
Also: yes some of those are on the JP side. That is what I mean by different worlds: it is quite possible that all 500K are densely concentrated across no more than 20 servers, and the other 40 servers are seeing few if any of these, while those on those 20 would say the world is as busy as ever. Without real numbers I can only guess, but that is the problem with trying to judge population density of the entire game, based on a few servers, or a specific timezone.
Not to nitpick but I think you missed the part where I said I am on "many" worlds and that is where I am coming from: each world I am on is different.
I am on significantly more than just Behemoth and not all of them are high density like that.