The *real* starvation response is very real. It's just not what most think. Most think it's, "you gain fat no matter what, even in a caloric deficit." No. That's not it.
But when you start dieting, your body is going to respond, period, and there's not much you can do to combat said response. You want to lose weight. Your metabolism if going to slow down.
The point is perhaps not whether or not we are in a calorie deficit when we gain or lose weight, because the very nature of weight loss is that there needs to be a calorie deficit. That part is clear. I think the REAL POINT is how low do we need to go to be IN a calorie deficit. In other words, if we need to eat 800 calories per day to be in a deficit (and thus to lose weight), then there is a PROBLEM. So if one is not losing on an 800 per day calorie level, then that means one's maintenance level is at 800. Now the real question is WHY? Why is that person's maintenance level so low?
My point is that yes, anyone can create a large enough calorie deficit to lose weight. We all know that if we dont eat, eventually we WILL lose fat. That is an absolute fact. But if it takes eating less than a reasonable amount to achieve a calorie deficit, we should be looking into why and trying to fix our system so that it burns calories quicker in order that our calorie deficit kicks in at a much more reasonable, higher calorie level (reasonable = satiates our hunger, gives us sufficient energy, and provides all the needed nutrients).