If his low frequency problem was causes by hydrops, he could absolutely see that kind of dramatic improvement in low frequency hearing.
Mine isn't caused by hydrops but Aldosterone should make my surviving strial Na/K channels (because it acts directly on them) more efficient and my cochlear electrolyte balance better. It can also help maximize receptor gene expression.
I don't think most people would benefit (although, Aldosterone or a low sodium, higher potassium diet does slow down hearing loss progression somewhat) but my specific case might see some benefit, possibly even a large benefit.
https://pubmed.ncbi.nlm.nih.gov/27157488/
I talked to the Canandian doctor who prescribed this for me at length and he said that very few people see a change in their hearing but the people who do have hydrops or very esoteric causes of hearing loss and they can see a very noticeable improvement after a few months.