Honestly this does seem like the case to me, coming from someone who's in a few all-flight servers. I think in these cases at least it's influenced by these servers being pretty old? So the initial communities these servers revolved around have thinned out as people have naturally lost interest in the game over time. That's not a bad thing, its normal, but it does mean these servers are having to rely on fresh blood for engagement. So if there's trouble retaining fresh blood then its gonna feel pretty meh.

Personally I used to be a highly active member in one of the servers I'm in, but a few years ago now I lost interest in the game. I've come back since and play on and off, but it isnt the same as it once was. There are some oldies in this server who's seemed to maintain regular levels of activity in it but honestly the majority of the people I remember being really active back in the day don't seem to be around anymore, or barely are at least. The server certainly isn't inactive by any means (over a thousand people after all) but it absolutely is a lot quieter than I remember it being.