This is the only time you'll face something like this, so don't worry.
About the actual boss fight
On the other hand, Khann himself is really easy. I don't know if that's good or bad for you, but for me—having tried to beat the gauntlets like 30 times—being able to defeat him on the first try felt like a gift
Have you tried using other crests? In my experience, certain crests make some fights ridiculously easy, while others can make them nearly impossible. The Wanderer’s Crest worked for me with this task, it let me take out enemies quickly and avoid getting overwhelmed.