I have a small fortune in bridal alteration books, so if you need help on something obscure, I can hunt it down.
https://www.youtube.com/channel/UCcXMGAm6Cx72kveyt9P6pBw is a bridal alteration channel.
@Missie that dress is a gal not wearing foundation garments and wanting the cups to do the lift work. The top is overly tight to get the decolletage, and the skirt is loose to skim the belly and not fold into the waist. The boning in these dresses is plastic and so if she pulled the waist tighter, the boning wouldn't really hold up and with heat of wearing, the plastic can warp and do funny things.
@BrendaP all my brides this year did not fit that mold. I actually had one between fittings I had to redo the darts because she gained.
All of the brides I worked with this year wore no foundation garments, and while most took my recommendation to buy a good fitting bra, I had one that did not. These were not sample size girls...I had to buy one dress form that adjusted (my personal one is a size 14, easy enough to pad to a 16 or 18 US sizing) that worked for a couple of girls, most were between the US sizing 22-26. All of them made a statement that if they were going to have the dress they wanted, they were going to be comfortable wearing it and did not want to wear anything under it.
Which is cool and all, but it can lead to some of the dresses not looking as we would expect.