I don't think you and I have a shared agreement of what metrics, cardio, and conditioning mean.
Here are what I think they mean, plus a few other points we seem not to have in common. At least at our respective points in our lives and our differing objectives.
Metrics: Hard numbers. In the case of general activities in this discussion, how much weight, how long, how many calories burned, what (if any % of Maximum Heart Rate [MHR]) a given episode of activities might contribute to conditioning objectives.
Cardio: An activity intentionally engaged in that elevates the heart rate (HR) to levels from 50% - 70% (LISS), 70% - 85% (moderate intensity), and 85% + (high intensity). Now mind you, I'm referring to classification tables that have been around since the 80's. I know there have been some changes since then, like LISS, which was regarded as something lower than whale shit back then when I was in my 30's. But AFAIK, these tables are still the way cardiovascular conditioning is assessed and classified. If you know better, hey, let me know. I'd be interested in knowing about something new and evaluating it.
Conditioning: Becoming fit enough to undertake medium to longer term continuous or episodic repetitive activities of low to vigorous intensity.
So how do we arrive at activities that elevate HR that provide an effect on conditioning? We do things. Do those things contribute anything? Maybe, maybe not. So we use sensors and the measurements and the metrics those sensors provide to evaluate the numbers against the classification tables and factor in the time factors needed or useful to produce a training effect. Again, if you know something different, fill me in. I'm going on information I've gleaned, collected, and evaluated over the last 50 years. But then I'm not an exercise physiologist or an SSC. So maybe I'm wrong about this and working on dated or erroneous information.
You're younger than I am, so you have to work way harder to get your HR into a training range you are looking to achieve. At 67, me? Not so much. My resting heart rate (RHR) is in the mid to upper 60's in bpm and my MHR is 153 bpm (Karvonen Method). This is a narrow gap to bridge especially if you look at the simple math involved. Which goes double when you are not and never have been an ultramarathoner with a low RHR. My RHR was in the mid 40's when I was in my 30's, and so time marches on and such things do not remain the same as you age. As you yourself may discover.
You seem to be conflating cardio with bodyfat and bodyweight as measured on a scale. Cardio can burn enough calories to lose bodyweight and bodyfat, and from the more recent research I have done, LISS seems to burn bodyfat better than HIIT. But then experts and advocates for both differ and contradict each other. In any event, your focus on 15% bodyfat seems more focused on aesthetics than conditioning. And that's fine too, if that's your primary objective. But it seems to me that cardio is not about bodyfat.
But when you get to my age and perhaps even well before then, you want to keep your heart healthy for longevity. Then too, I have my balancing act to maintain. Lifting, teaching and learning martial arts, tossing shit in the highland games, and conditioning is a tough bit of juggling at any age. The highland games is mainly for fun and a new challenge in my latter years. The other stuff is to live a good, long life effectively and safely.