If you don’t feel subjectively better after exercise than before, the solution is to add to the intensity and keep trying. I wonder what percentage of max heart rate he averaged.
Maybe some people feel better after exercise than before, but for the vast majority of people I've talked to, they're mostly exhausted after exercising. Same goes for me. And yes, I regularly exercise significant chunks of time at 80%+ of MHR.
And yes, I've done it for extended amounts of time, too. I've done half marathons. I've run somewhat decent times for my age. I was bored out of my skull while doing it. I certainly didn't feel a big endorphin rush.
Keep in mind that this doesn't mean "100% effort, 100% of the time". Rather, the body is extraordinarily effective in responding to brief sessions of intense activity.
For cardio, high intensity interval training (HIIT), and Tabata intervals in particular (20 seconds effort, 10 seconds recovery, repeated 8 times). This can be done with virtually any activity -- low-weight squats, rowing machine, sprints, burpbees, spinning, running.
For strength -- a small number of moderate-to-high weight sets (3-8 reps, 3-4 sets) -- 2-3x weekly, is more than sufficient to build muscle.
Long, low-intensity effort -- cardio or strength -- has relatively low yield . You can and generally should train efficiently.
The most important factor, though, is consistency over time. That is: get your workout in, and do that 2-3x a week, every week, year in and out. Rewards don't come from a heroic effort in a single workout, but consistency over time, with progressively (over weeks and months) greater challenges (more weight, effort, reps).
I asked my trainer if it ever gets any easier, in his words, "No, you just get stronger".
Feeling subjectively better after a workout session might be in the same line as "happens to some people".
One of my favorite recent book titles is "If You Like Exercise ... Chances Are You're Doing It Wrong: Proper Strength Training for Maximum Results"[0], which is another book about the work of exercise genius Arthur Jones, inventor of Nautilus and MedX equipment.
[0] https://www.amazon.com/Exercise-Chances-Youre-Doing-Wrong/dp...
[1] https://www.youtube.com/watch?v=F7GB3h82tcQ
[2] https://www.amazon.com/Body-Science-Research-Strength-Traini...