The new graphics API is not better in debug mode, but it allows you to do better things.
Example:
- if I draw 10000 individual sprites with sf::Sprite, I can get 50 FPs in release and 1 FPS in debug because there are 10000 OpenGL calls involved
- if I draw 10000 sprites with a single sf::VertexArray, I can get 350 FPS in both release and debug mode because there is 1 OpenGL call involved, it's the GPU which is busy not the CPU anymore