All of the Primal worlds are pretty balanced in population. According to the Lucky Bancho census, the difference between the lowest population (Lamia) and highest population (Leviathan) server on that datacenter is about 28%. In comparison, on Crystal the difference between the highest (Balmung) and lowest (Goblin) is about 84%.

Mind you, all of this may change on friday with Shadowbringers anyway so keep that in mind. And a whole bunch of new players have started since it came out so these numbers are likely all over the place anyhow.