Merlin sits next to 4 phonetic neighbors — Marlin, Myrddin, and Erlin are the closest matches by sound. Most share Merlin's Welsh cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"sea fortress"
"horn, strong-willed"
"chief, brave man"
"ancestor descendant"
"son of marsh dwellers"
"falling, rhythmic beat"
"flowing down, descend"
"darling, beloved"
"from Laurentum; laurel-crowned"
"son of the reeve, estate manager"
"avenger, one who does not forget"
"page boy, herald"
"settlement by the bridge"
"tile-maker, tiler"
"from Sweden, soft napped leather"
"firebrand, burning torch"
"wealthy protector"
"to tame, subdue"
"fifth born"
Similar sound: These names share phonetic patterns with Merlin — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Brittonic/Welsh origins, giving them the same cultural heritage as Merlin.
Rhythm: Merlin is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.