Not sure what you mean by 'avoiding mechanics'. Lost Vale worked as intended on Live, there were no exploits as far as I know. It was just overall pretty straightforward when it comes to dungeons.
And any game developer should rather focus on 'how can I make this engaging and fun' rather than 'how can i make this harder'. A good challenge is a method of engaging the player; like how you had to watch out for a minion of the Vulture Lord and kill him quickly before he came to his aid with a heal; The tank could not pull it, the DPS had to burst it before it reached the boss.