ROCm vs Vulkan has never been about performance - you should be able to represent the "same" shader code in either, and often they back onto the same compilers and optimizers anyway. If one is faster, that often means something has gone /wrong/.

The advantages for ROCm would be integration into existing codebases/engineer skillsets (e.g. porting an existing C++ implementation of something to the GPU with a few attributes and API calls rather than rewriting the core kernel in something like GLSL and all the management vulkan implies).