Energy system training has gained quite a bit of popularity in the CrossFit world over the last few years. It is apparent when you watch the best athletes compete at the games, they are all more well rounded than they have ever been before.
Energy system still really hasn’t made its way into the CrossFit class setting though because they are based off entertaining people not helping them reach elite levels of performance.
Most general population client would best off spending a few days a week performing aerobic capacity work (long steady state). The progressing to something more aerobic power based like above.