I agree with the improbability completely (not that I speak from authority, but your reasoning is sound).

That being said, there’s something about the depth of the ocean that has always fascinated me to the point where I teeter on the edge of “abandonment of reason”. Maybe it’s the child in me that wants these creatures to still exist, yet evade study in defiance of of humanity’s technical dominance, but I could sit for extended periods of time and let my imagination run wild with it.