I’m making something like the book case attached. I made the two “shelf” strips and put tenons on them with rounded ends.
I think what you are saying is that my design was ultimately flawed by a lack of joinery appreciation.
It’s certainly teaching me a lot. I have arched the tops of the end pieces and tried to chisel off the corners. As I did I ended up nearly smashing one of the sides off. This was again because I failed to work with the grain. A bit of sawing and rasping and I ended up with fairly decent curves.