I couldn't tell you how much impact this actually has, but Vulkan/D3D12/Metal have to be conservative with pipeline state changes, and have to manage the layout

I couldn't tell you how much impact this actually has, but Vulkan/D3D12/Metal have to be conservative with pipeline state changes, and have to manage the layout of various hardware data structures for you. They've gotten partway there with things like D3D12 descriptor heaps, but hardware-specific APIs just don't have those limitations.