You have the best way of phrasing things IK!
I have a small, lightweight, self-supporting chest (pencils are somehow supposed to stay? what?) in the 30C/30D/32B/32C range depending on brand, and I've yet to find a bra that feels even 20% as comfortable as going bra free. There isn't any drooping (yet!), not enough jiggle to bother me, and I get far sweatier with a bra than without. So I never wear a bra at home (where I spend most of my time). I only wear one when I go out (or for outfit photos here) if I'm wearing a fitted/clingy knit top sans topper, and thus the bralessness would be too obvious to casual observers (because both I would feel self-conscious and don't want to make other uncomfortable). In fact, I started loving & acquiring woven tops/dresses about 3 years ago, when I discovered how well they disguise things! It was the start of a revolution for me, hehe.
I'm just not willing to be in discomfort every day on the off chance it'll help the look of my bosom in 20 years. If they start to head south, I suppose I'll re-evaluate, but the older I get the more of a laid back hippie-type I seem to become, so I somehow doubt I'll care that much. I'll probably just wear more layers to disguise things. hehe Oddly enough, the initial desire for comfort ended up being very empowering: I no longer worry about looking flat chested/feel any need for padded bras, probably because I'm so used to how my chest looks on its own. I think of it as delicate now rather than small or flat, and I'm quite grateful for it, after having spent much of my post-puberty life feeling less of a woman due to that same delicacy.
If I were jogging I'd need a sports bra, which I remember whenever I'm with my niece and we start racing around, but the fastest I move in regular life is a brisk walk, and that's rare. I'm more of a strolling type.
I'm actually listening to an audiobook called Breasts: a Natural and Unnatural History right now, so this feels like a timely thread! If I learn anything about bras vs. gravity, I'll be sure to share it with the forum.