A zombie show on AMC is what's odd. It's not so strange that a violent, exciting zombie show somewhere on TV could be a big hit.
But asking people to accept a WWII Namor is asking for them to leap a few hurdles. Superhero shows work for a younger audience, while historical dramas appeal to an older premium cable crowd. How do you fit those jigsaw puzzles together? if the character were Captain America, maybe it could be done, since he fits the era wonderfully. But a half naked merman fighting Nazis? Sounds like Sat night SyFy movie.