We have Mars mapped. We don’t have a complete map of the ocean floor.
It’s a true statement.
Dunno why you say it’s hyperbole.
Mapping isn’t the only thing about “knowing”. We know far more about our oceans. We also do have them mapped. US subs operate with those charts, classified as those charts may be. We also have about 17,000 SOSUS sensors and nearly as many Buoys. The oceans are far from unknown. There have been tens of thousands of oceanic research operations throughout the oceans. We’ve laid tens of thousands of miles of undersea cables. We’ve created amazing 3-D mappings of the entire ocean floor.
Ignorance of all that is what leads to the hyperbole that we don’t know our oceans.
The dumbing down of America continues.