I've had an alt on Aegis for years, and I have no reason to believe it's a particularly low-pop server. I don't recall it being a Preferred world since I joined it, nor did I feel it behind in any way during Ishgardian Restoration (which I closely followed). I've still not seen queues over 1000 there, even at JST peak hours (7PM-11PM Tokyo time is what I've tested both the 10th and the 11th). Queues were around 500-700 trying to log in at these hours. Again, that's Japan Time. I've no idea what Aegis was like on launch day 1, 2 and 3. Didn't dare log off Malboro as it is my main.

So yes, I believe the experience and queues are massively different between worlds. My character on Behemoth starts seeing queues of up to 500 at 3PM EST, and they're up to 5000+ by 9PM EST. My character on Malboro sees similar queues, but they tend to start a bit later at 5PM EST.