Sion sits next to 3 phonetic neighbors — Shaun, Sean, and Shawn are the closest matches by sound. Most share Sion's Welsh cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"God is gracious"
"shining glory"
"red-haired, famous"
"keen ruler, bold king"
"slender, narrow"
"pleasant stream"
"stone ringfort, castle"
"God is my salvation"
"from the valley"
"holy one (of Dewi/David)"
"from the place of Einion"
"thunder"
Similar sound: These names share phonetic patterns with Sion — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Hebrew via Latin origins, giving them the same cultural heritage as Sion.
Rhythm: Sion is a 1-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.