No. The worst case scenario is 400 ppm, ie 400 grams per ton. It's soft mud, so you don't need to lift or crush rocks at all. Moving mass at sea is cheap. I think it can be comparably profitable to terrestial REE. Honestly, the only problem is Japanese business skill issues.
The whole rare earth under the seabed never passed the smell test. This story was passed around back as far as 2013.
You plan to pull a 50 ton rock off the ocean floor, send it to a terrestrial crusher to find the 1kg of rare earth material ?

