Results not as expected

IMO, you've learned something extremely useful from this, that I've seen people here unwilling to recognize (to the detriment of their odds of long-term success, IMO). I say this as a long term (17+ year) serious exerciser and masters athlete, with coaching education in my sport.

As a generality, each incremental increase in exercise intensity (such as walking faster) increases energy expenditure a small amount (i.e., burns more calories per minute). The increase in intensity minute-for-minute also increases accumulated fatigue, and increases recovery time needed . . . disproportionate to the increase in energy expenditure. More simply, increasing intensity increases calorie burn by a little (per minute), but increases fatigue/recovery-needs by a lot. There are diminishing returns for calorie burn, and increasing costs for fatigue/recovery.

Now, there's much, much more to it than that for athletes in formal training plans, but that fundamental idea is basic to decent athletic training plans.

For anyone, if the main goal is calorie burn, IMO there's a "sweet spot". You set your time budget for reasonably-enjoyable exercise, and you do it at the intensity you can sustain for that time period (with a little warm up and cool down if sufficiently intense), without feeling fatigued for the rest of the day. There may be a few minutes of a "whew" feeling right after the exercise, but you should feel energized, not depleted, for the rest of your day. (When very new, a person may not even be able to use their whole manageable exercise time budget right away, even at low intensity, so it can be good to gradually increase length and frequency of exercise sessions, if that's true.)

Becoming excessively fatigued from exercise can be counter-productive for weight loss. It tends to bleed calorie burn out of daily life. For example, we may sit/rest more, even sleep more because we're tired. We may drag through daily chores, make the simple dinner instead of the complicated one, put off or simplify chores and projects because we don't feel energetic enough to take them on. This can be pretty subtle! Maybe we just fidget less (research has shown fidgety people burning up to low hundreds more calories daily than otherwise similar but still/placid ones. We might choose not to window-shop, but watch TV instead, in free time. And so forth.

If excessively fatigued, to the point of dragging a bit, our daily activity burns fewer calories, maybe all day long . . . vs. the few extra calories the intensity added to our workout burn. It's pretty easy to wipe out a good-sized fraction of the extra burn from intense exercise. On top of that, very intense exercise inherently limits exercise duration: We can only keep it up for so long, even if quite fit (for physiological reasons even beyond fatigue); whereas after getting some base fitness in place, we can do low-intensity activities for a much longer duration, without becoming so fatigued that our body simply won't/can't keep going.

Sure, higher intensity exercise has benefits, physiologically. But, for fitness, someone relatively new to exercise is best served by getting good base aerobic fitness in place via lower-intensity exercise, which takes weeks to months depending on starting point, before integrating high intensity. (Note that the objective definition of "high intensity" varies depending on current fitness level.) Even then, true high intensity should be more of a condiment or side dish, in schedule terms, not a daily main meal. That's how smart athletes do it.

So: Good insight! Some folks who believe they have to do HIIT (high-intensity interval training) for long periods daily in order to lose weight would be smart to come to a similar insight, IMO.