Macsen sits next to 5 phonetic neighbors — Maxen, Mason, and Maxon are the closest matches by sound. Most share Macsen's Welsh cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"supreme, excellent"
"slender, narrow"
"high and mighty, chief"
"thunder"
"wolf"
"bold ruler, chief power"
"beautiful; fair"
"hedgerow, boundary"
"God is gracious"
"God is gracious (from Hebrew Yochanan via Welsh)"
"sad"
"holy one (of Dewi/David)"
"stone ringfort, castle"
"one who struggles with God"
"lover of churches"
"mighty hound, great wolf"
Similar sound: These names share phonetic patterns with Macsen — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Latin origins, giving them the same cultural heritage as Macsen.
Rhythm: Macsen is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.