I believe Aether is the top population of the entire game. I'm part of it on Balmung. I usually get duty finder matches instantly (but that's as tank, not DPS). It's also worth noting that the character creation restrictions seem to only apply to the creation of new characters. Paying $18 to transfer to another world seems to get around that one way or another (some have theorized it still honors the restrictions but is amazingly good at catching very short openings that occur).

I'd also ensure you're in your world's Novice Network, where you can ask for people to team up with you to queue faster for your duty. If it's a mostly-JP world, this may involve a lot of the auto-translate function.