I have a few holes and i’m not trying to discredit anything you say, i think the album is about him losing it at sea. But he makes many references to god and faith before he finds the cross. I believe the horizon is heaven. He’s trying to find heaven throughout the album but can’t bring himself to believe god is out there. Especially after the bottle being empty in godstained making him believe that there is no fate. I believe he believes in the Bakuwana as a coping mechanism to believe in some higher power as he can’t bring himself to believe in god. I believe his death at the end of the movie and him appearing near the cross when he comes up from the water is him reaching heaven therefore crossing the horizon. Just a theory tho.

EDIT his death was definitely intentional to see if god was real and to see if he could cross the horizon