I would put Debussy above Puccini without any problem...the latter is more of a populist composer ala Rachmaninov than a innovator ala Debussy and Mahler.
It is those “populists” who sell tickets. I am not a huge opera lover but I have to say Puccini had a hell of a lot of good tunes. I would also think Mahler is more highly considered than Debussy. Not by me.