Nobody needs all of Vulkan, but everyone needs quite a bit of it. Buffer allocation? Command encoding? Scheduling? Synchronization? Abstracting GPU architecture differences (and GPUs vary a lot)? Render pipeline fixed-function stages like primitive assembly, tiling, and blending? You're signing up to implement all of that - good luck!
In this view, your idea is the assertion, "I could do a better job at all that stuff than the driver developers." Maybe so! They're only human. Drivers do have bugs. But you're only human too.