Resistance training (esp HIIT) IMHO, is the most effective type of training to improve ones health ,not that cardio also doesn't have an important role, and if they focused on building lean mass they probably would have had better results.
I can't quite agree with that. First, high-intensity interval training is cardio, so I'm not sure what you meant by that. Second, I don't think a blanket statement that lifting is categorically "better" for health than cardio is defensible. It's going to vary a lot from person to person, based on individual circumstances and health status. Cardio is very overrated (and isn't even necessary) for weight loss purposes, but it has demonstrated health benefits. There are plenty of recreational and professional lifters out there whose health would improve more from an hour of cardio, than an extra hour of lifting, for example. Balance and moderation.
But having said that, yes, if I had to pick, the population concerned with body fat loss should generally focus more on resistance training than cardio. Ultimately, though, the best exercise regime is going to be whatever the person enjoys and is happy to stick with.
The assumption that you make that I disagree with is that the reduced activity level, after a typical caloric-restriction weight loss, is something that can be improved/increased with vigilance.
Of course it can. Unless you don't have volitional control over your body, you can choose to increase your activity level, in ways that do or do not involve exercise. This isn't necessary for weight maintenance, as you can also just consume fewer calories. Or you can do a combination of the two. But unless and until research demonstrates a way to prevent the unintentional reduction in activity (and, therefore, TDEE) that comes with loss of body mass, it's a reality of life. If research demonstrates that a particular dietary regime prevents this from happening, wonderful. But until then, it's something to be aware of, regardless of which dietary strategy is used to reduce weight.
The body reduces the metabolic rate for a reason and that reduction in metabolic rate is accompanied by a reduction in energy levels. To say that awareness and vigilance is the key is not really listening to what the body is trying to say and just continues to encourage people to fight their body instead of listening to their body.
I don't know what you mean with your claim that increasing your activity level is "fighting your body" or "not listening to your body." If I take the stairs at work instead of the elevator, I don't consider that "fighting" my body. Same for standing while talking on the phone instead of sitting. Or walking to the corner store instead of driving. If someone prefers to maintain a lower activity level (or must, because of injury or other condition), then the calorie consumption has to be correspondingly lower.
Unless definitive contrary research comes down the pike, losing weight through whatever means results in a lower total daily calorie burn, compared to someone with equivalent body composition who did not diet down to that point. Some of that reduction in energy expenditure is hormonal and we don't yet know if it can be prevented, or how. Most
of the lower TDEE, however, is from unintentional reduction in activity level, and more efficient movement that uses less energy
. With a reduction in TDEE, we have to move around a little more, eat slightly fewer calories, or both.
There's a lot of money and prestige to be earned for whomever demonstrates how to prevent this from happening in the first place, or how to ameliorate its effects without increased activity or reduced calorie intake. Until then, though, it remains wishful thinking or merely guesswork.
EDIT: Adding, the big picture here is that once someone has lost a significant amount of weight, their RMR is going to be lower anyway simply because of the change in mass. So to maintain the lower mass, that person will already be consuming fewer calories than before the weight loss, and/or increasing total activity. The marginal reduction in RMR only changes that by a small amount.