You’re right, though I suspect you could increase that “max” current figure quite substantially if we’re assuming this is an underwater ROV and the wire has water cooling for free. You’d need to be pumping a whopping 300A/mm^2 through that wire to match the 150W fiber, though, so your conclusion isn’t affected.

Also, your calculation is for equivalent diameters. If mass was more important then, well, the fiber is 1/3 the density of copper…