I’ve been training and working with athletes in some capacity for now 20 years. And what I’ve found is this: of all the variables I have to manipulate as a coach: sets, reps; tempo; speed of contraction; exercise selection; sequence of events; vertical or horizontal loading; one set or multiple sets; frequency of training: all those variables have their own benefits and drawbacks. There’s not one perfect variable.
Additionally, each athlete has a specific sport; position; injury history; training history; training age; different genetics; neurological biases; response to stress; response to specific means as well as specific methods; recovery abilities; bias to different parts of the force-velocity curve; and accommodates at different rates.
So if there cannot exist one perfect variable, there cannot exist a perfect program. So it is a science, and an ART of how that science is applied to athletes. Training must be individualized, and adjusted even on a daily basis. Otherwise training is just an excel document to run through, and every athlete who’s not the genetically gifted “freak”, eventually fails out.