I know, I know. 
This is what I would recommend myself to a lot of people.
For context: In my 20s, I trained up to 6 hours per day with 2-4 sessions per day (A mix of general conditioning aka the OG of “CrossFit” and various martial arts). So, I’ll have to slowly change my mindset.
Let me get a bit existential here: Whatever you do, you do in a particular manner and as both a positive decision (I will do this) and negative decisions (I don’t do this and that and…).
- Manner I like to be serious about everything that I do, since I think this is the correct way to conduct yourself. When I train, I train to the best of my ability (not all out hardcore, but aiming for the perfect and desired stimulus). When I spend time with my daughter (2y), I try my best to be positive (fun, providing sense of security and calm, etc.) and demanding (I always try to merge positive emotions with learning and training with her). When I talk with my wife, I try to hyperfocus on what she says and use my complete brain (yes, I know the 10%-usage-myth) to engage with her.
- Decision It is Sunday morning. I woke up early, my family is sleeping. What do I do? Chill and watch some meaningless series? Or: Do I listen to empirical cycling, cross-reference the studies and work in the learnings into my training schedule? I do the later. I don’t stress about it, I just think it makes more sense and I have a better time like it.
Based on this, I don’t think “just do whatever” is a good way to engage with anything, unless you just have to get going. It is rather style of low-living instead of high-living.
So, right now, I am building “the perfect” cardio regimen and therefore try to learn as much as I can from the most numbers-based endurance domain that I could find: Cycling.
In the end, I agree: Get the volume in with easy sessions (endurance, zone 2, whatever you want to call it) and have 1-3 hard sessions per week to top it off. So, I only have to gain by going unnecessarily deep. 