NA: Can it be serious?

Can a heavier topic like drama or historical fiction be NA if it is about angsty self-discovery of what it means to survive in the adult world .... but also if it features a male protagonist and is not a romance? Henry II was 17 when he inherited and Edward IV was 19. Topic-wise, the stories of either of their ascensions fundamentally focuses on someone abruptly forced to deal with the adult world. For fantasy readers, we're talking the Robb Stark "I must stand up because my father was wrongly killed" story arc here, which bears an uncanny resemblance to Edward IV's actual one, when his father, Duke of Stark York was murdered by Lannisters Lancasters.

NA seems to be defined by "self-defining" type angst of coming of age and trying to find your place in the big world... which actually does describe the whole "big shoes to fill / heavy is the head" situation most of abruptly ascended medieval teenage kings were abruptly thrust into. What confuses me is that that's been a valid adult historical topic for ages, and NA is usually petty crap about sex in college, not world-scope sweeping-political-ramifications coming of age.

Is there an accepted "tone" for NA? The same way YA is usually about misfit high school angst and is separated in tone from adult by just not being as dark or gritty... Even if we followed Henry II's early campaigns to reclaim his mother's throne at 14, it would be adult automatically, not YA, because of content. But since NA does allow the gritty stuff and is explicitly supposed to be about angsty self-discovery and finding one's place in the world, would something that large and heavy in scope qualify? Or does it get bumped up to Adult because NA is supposed to be fluffy romance, and therefore NA Historical implies bodice-ripping?