At least going by my experience with a couple of similar-sized HDX 7s a few years ago, I would agree with you regarding the point of it being more ideal for casual consumption. I don't even think it's down to a difference in weight so much as the fact that smaller devices are so much easier to use just in terms of picking up and carrying around.
I'm really looking forward to getting my new mini.
Yeah even at the same weight as a larger device, a smaller device has a center of mass closer to your hand making it easier to hold, and a smaller device is obviously more weildy as it takes up less space, and I think there is a mental aspect as well—the smaller size makes it mentally more “approachable” and “casual”. But of course, bigger screens have their advantages too. So it’s about balance. The right balance is very subjective—depends on the function, depends on the person—but I think the mini hits a balance that a lot of people find ideal or close to ideal for casual consumption, especially reading.