where did the 70s take the horses
I think Ms Raini, (the OP) did an very good job on her assessment and explanation.
Anyone who's owned and/or regularly driven examples from the various years- say a 66, a 67, a 73, an 86, and a 92, can attest to the same findings.
The bottom line is- it didn't go anywhere.
9.x compression to 8.x compression, then back to 9.x (LA roller), then back to 8.x (Magnum), and all very similar cams (until Magnum) also proves "it's all in the heads".