That's something of a sweeping generalization. Zink has managed to beat a native OpenGL driver in some particular benchmarks.

In many other benchmarks, it loses. That being said, it still manages decent performance, which is extremely impressive for a one man project using only the Vulkan interface. It wouldn't surprise me if it eventually becomes the default OpenGL driver in the open source driver stack (for HW capable enough to support a Vulkan driver, obviously).