1) Princesses getting engaged young was ENTIRELY common practice for a long time, so it's mostly meant to BE historically relevant (either because the setting actually is in that time, or the setting wants to hearken back to it)

2) Yes, it's a war crime, and that is USUALLY the point. That it's meant to establish that the setting is DEEPLY SCREWED UP, or that the one who recruited the teenagers is NOT exactly moral.

3) Love is often insecure.

As seen with Din Djarin and Bo-Katan Kryze using the Darksaber, and Sabine with Ezra's saber, Mandalorians are about the only other group who can effectively capitalize on the Lightsaber's offensive ability thanks to Beskar armor.

While true, that also depends immensely on who you ask. There's plenty of people who consider Oppenheimer a monster for creating the Atomic Bomb, just like there's no doubt those who see Jetrel as one

That depends on who you ask. There's lots of people who still consider Oppenheimer and the rest of the Manhattan Project as war criminals because of what they unleashed with the atomic bomb.