> The performance of any application on SYCL is currently quite poor.
SYCL can get pretty much equivalent performance in Kernels to eg. CUDA. Try looking at SYCL performance papers on Arxiv. Eg. see [1].
That isn't to say that SYCL code is optimised on every platform without tweaking - you do still need to put effort into target specific optimizations to get the best performance, like you would in the CUDA or HIP.
> Why drop ROCm (used on the world's largest supercomputer?)
Some of the world's largest super-computers / HPC applications do use SYCL for AMD! The application I'm most aware of for this is GROMACS. As to why? - because having 3 version of the same code using different programming APIs is a big maintenance burden.