Tony Asher was the real genius behind Pet Sounds and, as you noted, lifted up Brian’s creation from bubblegum to something with more substance.
It’s kind of hard for me to give all the credit to a guy whose work outside of Wilson was commercial jingles and The Partridge Family.
His major value to Brian was being:
1. A talented lyricist
2. Who was not Mike Love
Weirdly, the best contribution on that record may have been from the Ringo of the group - Al Jardine. He’s the one that took Sloop John B to Brian and worked with him on the arrangements.