Here are some errors / warnings that I noticed (abridged):

witcher3_d3d11.log:

err:   D3D11: Invalid blend factor: 1042108203
err:   D3D11: Invalid blend factor: 1492957192
err:   D3D11: Invalid blend op: 4100
err:   D3D11: Invalid blend factor: 1073889088
err:   D3D11: Invalid blend op: 1042108203
err:   D3D11: Invalid blend factor: 1049700610
err:   D3D11: Invalid blend op: 1046135251
err:   D3D11: Invalid blend factor: 1086918619
err:   D3D11: Invalid blend op: 1040187392
err:   D3D11: Invalid blend op: -2109401936
err:   D3D11: Invalid blend factor: 32720
err:   D3D11: Invalid blend factor: 41301646
err:   D3D11: Invalid blend factor: 1073889088
err:   D3D11: Invalid blend op: 1042108203
err:   D3D11: Invalid blend factor: 1049700610
err:   D3D11: Invalid blend op: 1046135251
err:   D3D11: Invalid blend factor: 1086918619
err:   D3D11: Invalid blend op: 1040187392
err:   D3D11: Invalid blend op: -2109401936
err:   D3D11: Invalid blend factor: 32720
err:   D3D11: Invalid blend factor: 41301646
err:   D3D11: Invalid blend factor: 1073889088
err:   D3D11: Invalid blend op: 1042108203
err:   D3D11: Invalid blend factor: 1049700610
err:   D3D11: Invalid blend op: 1046135251
err:   D3D11: Invalid blend factor: 1086918619
err:   D3D11: Invalid blend op: 1040187392
err:   D3D11: Invalid blend op: -2109401936
err:   D3D11: Invalid blend factor: 32720
err:   D3D11: Invalid blend factor: 41301646
err:   DxbcCompiler: Unsupported operand type declaration: DxbcOperandType::InputPrimitiveId
err:   DxbcCompiler: Unhandled operand type: DxbcOperandType::InputPrimitiveId
err:   DxbcCompiler: Unhandled PS SV input: DxbcSystemValue::PrimitiveId
warn:  D3D11Device: No matching border color found for (1e+010,1e+010,1e+010,1e+010)
err:   DxvkGraphicsPipeline: Failed to compile pipeline

witcher3_dxgi.log:

warn:  DxgiAdapter: DXGI_FORMAT_D24_UNORM_S8_UINT -> VK_FORMAT_D32_SFLOAT_S8_UINT                                                                                                            
warn:  Vulkan extension VK_KHR_maintenance2 not supported                                                                                                                                    
warn:  DxgiFactory::MakeWindowAssociation: Ignoring flags

I genuinely don't care

It sounds like there is a lot of variation between vulkan drivers. And I get it why it's a pain to deal with from support perspective. But why for example Vega isn't a good target? I suppose it should be more common for AMD users going forward. Of course testing it without actual hardware is probably impossible. But if you for instance make some crowdfunding for such support, I suppose AMD users can help you to get recent cards :)

Vega cards work well with RADV from mesa-git.

I know trying to deal with AMDVLK is a pain, specially since they've made it a habit of breaking things every other week, but since it's the same code used for their Windows driver, it's the only way to support DXVK on Windows (I know, not the most useful target platform, but still nice for benchmarks...).

However, i think it's currently a problem on AMDVLK's side, since DXVK used to work well on it before the Vulkan 1.1 code drop.