I am more incline to suspect that the original Bismarck was some form of Allag construct, perhaps a chimera or even some form of Allagan vessel. After all the Vanu Vanu claim that he carried them to the Sea of Clouds from where they were persecuted. The thing with Bismarck is we have two separate people with legends related to him and clearly they must have some shared origin. I am not particularly convinced the Allag would create a primal that wasn't locked up. They knew the inherent problems with primals.

One theory I had was that Bismarck was literally an Allagan warship with submersible capabilities that travelled between underwater Allagan instillations and places like Azys Lla. A white sub traveling under the water and destroying any vessels that wondered too close to important Allag installations could easily be mistaken for some kind of Whale by seafarers, particularly if they were less technologically savvy and living outside Allagan society.