Most influential at this stage was architect William Playfair, and his flair can be seen in many of the streets and public buildings of the time.
William Playfair was most influential because of his father's legacy. 
mnli hypothesis: William Playfair was most influential because of his father's legacy.  premise: Most influential at this stage was architect William Playfair, and his flair can be seen in many of the streets and public buildings of the time.