I think the reverse is true- cardio productivity would either be unaffected, or even improved, by using headphones, as opposed to "brutal concentration".
Why? Cause when you're bored and plodding away, your mind is going to travel to your worries of the day. You're going to think about what's next (natural when doing tedious thigns). This leads to elevated stress levels (as most of us face stressors in everyday life) and higher cortisol levels.
When you're zoned out with some B.I.G. or some jigga rattlig your ears, you're not thinking about work crisii or relationship woes. you're focusing on money hoes and clothes- all the runner knows. You're already taxing your CNS with the cardio, so let your mind be at ease.