Yates just used the pyramid principle solely in his later years. Nothing radical.
In his early years Yates used not just pyramid sets but also straight sets and reverse sets. This is what his old chest routine looked like back in the 80's.
Bench press 135x10 200x8 265x8 285x7 310x5 pyramid sets
Incline press 250x5 240x5 230x5 reverse sets
Incline flys 70x8 70x7 70x6 straight sets
Source: his 1985 to 1990 journal files
So you see, he did various traditional methods to build up and not hit.