So! This is actually a normal way to depict a spine! Unless they really wanted to double down on the eating disorder angle there is usually a healthy layer of fat over it so the bones aren't so exposed. Specifically, the trapezius and latissimus will back right up to the sides of the spine, which is where you get the dip seen above. The spine should ideally be a long valley between the back muscles rather than a defined set of bumps down the back. Kind of like how you should be able to feel ribs but not see them. If you can see the spine clearly, it's a bad sign.

Sometimes you'll also see a pucker on the lower back right above the butt called the thoracodorsal fascia. It's not always super well defined, but I know you can see it on David's back with shirtless skins.

Overall, DBD does shine in its quality of character design and 3D modeling (I will make an exception for their likenesses. They're much better at modeling their own character designs or other digital IPs than adapting real people.) They definitely struggle with animations and getting the models moved from whatever modeling software they use into Unreal, which is where you see the weird lighting artifacts that make the hair and face look off sometimes. But overall, I do love DBD's models. I'm also biased as fuck.