The US National Library of medicine National Institutes of health published a medical article “The effect of Strength Training on estimates of mitochondrial density and distribution throughout muscle fibers.”
The article concluded that “muscle hypertrophy associated with strength training results in reduced density of regionally distributed mitochondria”
This does not mean mitochondria are not produced from strength training, but it does mean that the density of the mitochondria is not as dense as those produced by cardio.
The healthier the mitochondria, or more dense in this case, the better fat and sugar burn during your workout. As a result of increased fat and sugar burn the more ATP energy will be produced to fuel your workout.
Moral of the story, don’t skip the cardio, whether it’s steady state cardio or high intensity.