Check out the arc where they went on dungeon crawling on elven island, they were definitely on the idea to exterminate all humans, because their lifespan and magic use technically would make them superior species.
Also, they have flying ships but condoms is a lost tech I suppose...
That wasn't all of them... it was some of them....
And the reason they didn't need condoms is because it was almost impossible for them to be impregnated by humans...
Basically, humans don't need condoms when having sex with elves... because the chance is so low that it's a miracle...
That said, while it's true they have flying ships, their technological level is actually pretty low... the ships seem to be powered by magic (remember, this world has naturally floating islands).
So for them, flying ships and battle armor is much easier to produce.
Plus, in general, they'd normally want more kids. Only exception is when they become too old... and for that, they can purchase the services of other races... it's probably even safer than condoms...