Is “what's more” associated with AI writing?
Weak-to-moderate signal, stacking transitions that add to AI's connective density.
Why it sounds artificial
Individually human; collectively (with moreover/furthermore/additionally) they form the connective tissue of generated prose.
What to say instead of “what's more”
Example rewrite
What's more, the fees increased. To make matters worse, service declined.
Fees went up while service got worse, the two lines crossed in March.
Check your own text for “what's more”
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