Why distinct letters help early
A five-letter guess without repeats can test five separate characters in one turn. When little is known, that usually produces broader evidence than spending two tiles on the same letter. The advantage is coverage, not magic: an uncommon set of five letters can still reveal less than a thoughtfully chosen word built from characters that recur throughout the playable dictionary.
Position matters too. Discovering that S exists is useful; testing it in a place where many surviving words actually use S is better. For a candidate family rather than a blank board, paste the survivors into the Word Frequency Analyzer.