If you are referring basically to the last half of the 19th century-early 20th for that to be true you would have to throw out Puccini. I also prefer Richard Strauss but I’m drawn to bombast. I got to see Ein Heldenleiben this season by the CSO at Orchestra Hall. The sound of that orchestra is the closest one can get to Heaven and still be mortal.
Assuming your statement is true my point is that the former were the greatest of all generations. At least as classical music is concerned.
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.