I remember A2 Insurgency server being full all the time, just sayin. Eh, good ol' days.
That popularity(quantity) comes with no quality at all. All that players are typically lone wolfs and jumping in jet/attack heli as soon as possible ("hey guys, do you need cas?" in chat while hovering 100m above us in hot AO in Commanche without gunner, true story), and they are often 'activate' AOs all over the map, which again leads to poor performance. It's popular partly because there is no rules and no control. Also not everyone have Apex DLC with Tanoa to play on second server (main reason it's not that crowded) and this is why I'm talking about BMR Insurgency with Altis (vanilla, only base game needed) for first server.
Every time I'm on Liberation server it's always one big mess. Gigantic FOBs with abandoned trucks and tanks, AI squads waiting for their master (who d/c a while ago, yesterday I saw two fully packed MRAPs just sitting way beyond frontline and not moving). Enemies teleporting and ignoring half of the mag in torso (their spawn is often broken aswell, yesterday we walked up to the center of big town and T-100 with infantry literally spawned on top of us), helis taking like 4-5 AA missile hits to go down (single hit must be enough) and teleporting in the air, again due to lag and bugs. LIberation scenario itself isn't that good, and AI ratio just not suited for non-full server - 4-5 players vs. tank platoons?
Why that issues didn't pop up here before? No idea.
Anyway, BMR Insurgency have none of this problems. With a little bit of tuning of parameters it will be ideal, I think. But it's up to you to decide, I'm just giving ideas.