There is plenty of literature to show the body has 3 main energy systems (phosphagen, glycolytic - aka anaerobic, and mitochondrial respiration aka aerobic), an

There is plenty of literature to show the body has 3 main energy systems (phosphagen, glycolytic - aka anaerobic, and mitochondrial respiration aka aerobic), and many activities are a combination of all these energy systems. Further, doing pure anaerobic activities without warmups (which are more aerobic in nature) would increase injury risk; whilst low intensity/aerobic oriented activities have been shown to improve general health and well being, which would also be important to maintain an athlete's ability to train over a longer period of time. So perhaps it's not as polar nor "time" wasting as you think as you think.