Duffie sits next to 3 phonetic neighbors — Duffy, Daffy, and Trudy are the closest matches by sound. Most share Duffie's Scottish cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"dark one, descendant of Dubhthach"
"the bitter one"
"garland, wreath of victory"
"hero, man of courage"
"sunray, shining light"
"variant of Geraldine"
"famous in battle (via Clothilde)"
"victory of the people"
"strong"
"victorious one"
"famous"
"settlement in the valley, valley town"
Similar sound: These names share phonetic patterns with Duffie — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Irish Gaelic origins, giving them the same cultural heritage as Duffie.
Rhythm: Duffie is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.