Yeah, regeneration thing was kind of a bummer. Especially since it was his head and not like blown off his arms and other limbs that could be plausible. To your point, I was kind of hoping the ejection seat wasn't a thing. To piggyback your story telling, his battle he was fighting is that he was a coward and let his country down as a kamikaze pilot, I think his redemption would have been a solid ending. If they wanted to keep adding dread to the movie, they could even show Noriko alive at the end, and tell her what Shikishima did for his country.
Him sacrificing goes against the entire movie that is anti-war and telling you the Japanese government told its soldiers to needlessly sacrifice themselves. The entire ending is the citizens of Japan banding together without the help of any government to collectively protect themselves.
Here’s how they could easily fix it: him dying undermines the Dr’s monologue about being careless with life, which is the better message and what the movie is about/after. I think the true answer is to keep the ejection seat, but leave Noriko dead.
Damn, my Kong/Godzilla penis size chart image isn't there anymore https://forum.chorus.fm/threads/godzilla-vs-kong-march-31-2021.16740/page-7#post-4260578
Oh no Zilla, we gotta have Die Hard taking 3 Dolby slots this weekend and the Beyoncé concert film taking up the 4th