He was against incline pec presses in his later years but if you look at his pec through the years his muscle mass in his upper pec definitely dissipated because of that. He did sing the praises of the decline just like Yates.
He was against anything old school & anything that wasn't going to help sales of his E-book which as far as I know was never published as a real hard cover book.
If you look in most gyms the flat bench is still the most popular amongst hard core trainers.
I train now primarily at home but when I was in the gym I hardly ever saw anyone use the decline bench, dip machines or free dips yes.
Lying head down is just not a good feeling for most people.