excellence, talented person
儁 centers on outstanding human quality: excellence and a person of exceptional talent.
儁 combines the person radical 亻 with 雋, which likely contributes both sound and the idea of excellence or distinction. The exact historical development is uncertain.
A person 亻 beside the rare component 雋, which looks like a bird 隹 with an extra mark, suggesting a standout individual—someone marked for excellence.
For シュン, imagine a talented person named Shun who is always chosen for excellence: Shun -> シュン.