If we haggle too much over what creature is marked by the nickname Leviathan, we would miss the point entirely here. Should we need something approaching a literal animal, a crocodile or any of the larger sea creatures seen from time to time would suffice. In the minds of Job and his people, there need be no particular distinction between them. Leviathan is partly legendary by necessity for a desert-dwelling folk.
We have noted already that God would not hesitate to use whatever tool is needed to get His point across. It simply is not possible for any human language to express directly what God is, much less what He thinks. Parabolic expression is the only way for God to speak, for it is our Creator addressing human mortality. Not only do we not reach outside our time-space prison, but we are fallen within it. The human mind cannot comprehend anything about God, so all discussion of Him can only be indicative, using symbolic logic.
Thus, the creature seems a bit fantastic for a pedantic literal reading. But the implication is obvious: There is much inside our time-space bubble that we cannot comprehend, much less handle directly. How could we pretend to operate on God’s level where He stands outside that bubble? We would be more successful wrestling a fire-breathing monster with impenetrable armor than to argue with God. At least we could physically approach Leviathan, in theory at least, but God is rooted outside our realm of existence. And even with today’s unspeakable weaponry, we still could not create such beasts from our limited understanding of what can and cannot live in this fallen realm of existence. That’s because we do no comprehend the fundamental moral fabric woven into all of Creation in the first place, the moral character of God Himself.