Arwyn sits next to 4 phonetic neighbors — Arwen, Arvin, and Erwin are the closest matches by sound. Most share Arwyn's Welsh cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"very white, very fair"
"clear, luminous person"
"path, road, way"
"old river; slow-flowing water"
"from the valley"
"contentment (as Reza in Persian)"
"an extremely large, uncountable number; boundless"
Similar sound: These names share phonetic patterns with Arwyn — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Welsh origins, giving them the same cultural heritage as Arwyn.
Rhythm: Arwyn is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.