Fitness is a lot like sailing. Spend more time on the water and you get better at it. There is nothing new here, just a fad.
Go to the gym and do ANYTHING and you will get fitter.
With weights you are better off with good form rather than heavier and if you keep at it without too long for recovery in between sets the heart rate is kept up and cardio gains are made.
Aerobic is a constant so it it anaerobic that makes gain and promotes recovery time.