Coming back to this briefly. I believe this is why Guyver had a better chance in the American markets.
Because overall, what you have with Guyver is a pretty classic case of a superhero story. Think about it.
Young boy in highschool, gets endowed with incredible powers. And is then thrust into a world of terrible monsters, evil villains, etc.
You can so easily make it work in America so long as an adaption is respectful to the source material, and is completely made.