Aether has two very overpopulated servers and several mid and low pop servers, and Primal has several high pop servers and a few med/low. So it balances out. They each have a few preferred servers at the moment.

Adamantoise is a preferred world, so it should have a star - probably only in character creation, if you aren't looking there. It doesn't matter anyways; you don't get anything out of higher population except more afk people sitting around, it doesn't affect your gameplay in any way. It may be quieter, but none are dead or anything.