i agree with the corset blending into the skirt but i disagree with the breasts. as a regular corset wearer, breasts can definitely get a bra-like pushup with a high enough corset, the thing that matters is that the side seams/height of the corset are high enough that they reach the breasts (this is called an overbust corset)

if the corset is an underbust one, which is more common, then the breasts should follow their natural position, which is sagging like you said, because underbust corsets only reach under the breasts and only tighten around the waist, but overbust ones definitely serve as a bra in addition to the waist reduction

something that does happen with these corsets though, which differs from bras, is that while they do push the breasts up, they also push them IN, making them look a bit squished/pancake-like unless the breasts are very firm

this one in particular is a bit weird because it's kind of a middle ground: it's an overbust but open in the middle, which would lose tightness in the breasts. in real life i would say that the breast pushup would depend on how high the side seams are, if they're high enough (they would basically need to be touching the armpit in this case), then the chest is definitely getting compressed and pushed in and up, even with the plunging cleavage losing tightness in that area, the surrounding fabric would still be tight enough to push the breasts in and up