[shawkinaw]

I guess it depends what you mean by "waste heat". I consider the waste heat as the "extra" heat/energy on top of the heat moved. But even if you consider all the heat as waste heat, calling 30% more "far" more seems like an exaggeration.

[MrGilbert]

Depends on the reference. If the underwater datacenter produces only e.g. 3% atop, 30% is still "far more".

But without scientific sources, these are only wild speculations.