By delaying the introduction of content to duty finder, you increase the odds of successful duty finder attempts than if it had been implemented in DF straight away.
When leviathan came out, the only way to learn it was through party finder for a good few weeks, when it was released in the Duty Finder, I found it had the highest success rate of any extreme I've done through the duty finder, generally almost every group killed it.
Why? Because the general population was more knowledgeable about the fight before entering the Duty Finder, it resulted in more successful groups, essentially increasing the success rate of Duty Finder.
I'd say it's a worthwhile price to pay.