I still think it's unfair, and thus unreasonable, to have the rank up test depend so heavily on the miners, but on the other hand it's necessary to get the valuable minerals from a dungeon doomed to disappear once conquered. So, you might say it's a necessary evil. However, that being the situation, conquering a dungeon shouldn't be used as rank up test in the first place. If mining the place is more important than testing the adventurers, then having it as the test is putting the horse before the cart. Arrange another kind of test and make guarding the miners and conquering the dungeon merely a mission. Considering you get new skills from conquering a dungeon, there should be no end to adventurers wanting to do it.