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"
"bright fame"
"keen ruler, bold king"
"hedgerow, boundary"
"from the valley"
"first of the month, calends"
"from the place of Einion"
"circular stone fortress"
"gift of Isis"
"beloved"
"fort, castle"
"supreme, excellent"
"God is gracious (from Hebrew Yochanan via Welsh)"
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.