The genre of Job
The book of Job falls clearly in the category of wisdom literature:
Wisdom literature is a genre of literature common in the Ancient Near East. This genre is characterized by sayings of wisdom intended to teach about divinity and about virtue. The key principle of wisdom literature is that while techniques of traditional story-telling are used, books also presume to offer insight and wisdom about nature and reality.—Wikipedia
So the core of the genre is sayings that have a larger meaning than what lies on the surface. We still use these sorts of sayings:
A bird in the hand is worth two in the bush.
One sees the greater truth of the saying even if you aren't a bird hunter. Testing the accuracy of the proverb MythBusters-style misses the entire point. In wisdom literature, the image painted by the words is designed to be vivid in order to aid memory. Therefore the details of the sayings need not relate to any present reality; when God mentions "the young women in your house", He isn't thinking of Job's daughters, but of generic "young women". Certainly the saying works on an abstract level even for people who don't have daughters.
The prose frame
While the bulk of Job consists of speeches filled with proverbial sayings, the first two chapters and the short epilogue are written in prose and bear similarities to the narrative style of other books such as Ruth, Esther, and much of Genesis (particularly the Joseph story). There is strong evidence that the prose portions of Job were added later in order to frame the speeches. If so, the details of the sayings were settled before the details of the narrative were.
Alternatively, the narrative frame could introduce Job as a parable. In this scenario, Job was never intended to be a historical figure, but to pose a meta-physical question: Are righteousness and suffering antithetical states of being? The parable asserts that Job embodies both states at once. The speeches conclude with God asserting His mastery over creation and, I believe, evil itself.
God tames evil
Now what is the point of the proverbial saying? As you mention, the context is Leviathan, which was a symbol of chaos. God asks a rhetorical question of Job: "Can you tame chaos?" The answer is clearly no given the context of the framing narrative. It's especially poignant when you compare this proverb to what Job actually did to prevent evil:
His sons used to go and hold a feast in the house of each one on his day, and they would send and invite their three sisters to eat and drink with them. And when the days of the feast had run their course, Job would send and consecrate them, and he would rise early in the morning and offer burnt offerings according to the number of them all. For Job said, “It may be that my children have sinned, and cursed God in their hearts.” Thus Job did continually.—Job 1:4-5 (ESV)
He preemptively sacrificed in order to atone for sin that may never have occurred! Even a man as righteous as Job cannot reign in the effects of disorder in the creation. As hard as it might be, it could be that God chose His words carefully in order to remind Job of his ineffectual sacrifices. Frankly, the book of Job is what we sometimes call a hard word. Other parts of the Bible (such as Isaiah, Daniel, and Revelation) soften that word by revealing a future in which God binds up evil, puts away suffering, and defeats death.