I'm curious what professional GPU use cases you have in mind? I'm not as familiar, but ML has a pretty good lead with Nvidia/CUDA. I work in VFX. Nvidia Quadro cards have been fairly standard for more than a decade and didn't have a lock-in like CUDA (outside of the Linux driver support). In the past couple years Redshift has been the only prominent GPU renderer and it uses CUDA.

Honestly, those are the only professional use-cases for multiple GPUs I'm aware of. CAD uses GPUs, but not multiple and I don't see AMD having any lead over Nvidia. Same with other uses like GPU acceleration in things like Photoshop or video editing--1 decently fast consumer grade GPU is enough. I don't see farms and 4+ cards per box.