The blue battles were supposed to be hard, according to the pop up. The fact that most blue battle can be brute forced easily instead of using some specialized team at the minimal level required to enter the instance is the REAL problem.

Personally, as I had no immediate need for coupon and that's all it really gives (other than an equipment upgrade mat that I can't sweep for as a result but I had no use for it because the game refuse to drop sages for me, I've cleared 80 for about 2 month now, only 2 drop. wth game! /endrant), so I delayed until I leveled up a bit more, I think I beat it 2 levels later or so easily w/o using any special team, probably around 23/24k at the time. And yes, there are special tactics that focus on interrupt etc that will pass it even earlier. There is nothing wrong with it.