I’ve not watched the documentary you mentioned but I object to the idea that Lovecraft really founded any genre. Sure, his mythos has a cool aesthetic which has been used by others but the idea of a that wisdom/knowledge is linked with madness. Just look at the Odyssey. Odysseus has himself chained to his mast to gain knowledge of what the siren song.

You’re totally right. Many of his stories fixate in the horrors of the ocean. I’d go as far to say that’s his defining aesthetic, though hardly and original one. See monsters are as old as time.

Basically, imo Lovecraft is a hack who is only famous because other artists drew Cthulhu to look cool.