Perhaps RDNA3 GPUs get comparable results, but RDNA2 GPUs are behind.
I bought a RX 6800XT to do some AI work because of the 16GB VRAM, and while the VRAM allows me to do stuff that my 6GB RTX 2060 wasn't able to, on performance side it's actually a downgrade in many aspects.
But the main issue is software support. To get acceptable performance you need to use ROCm, which is Linux only. There was some Windows release of ROCm few weeks ago, but I am not sure how usable it is and none of the libraries have picked up on it yet.
Even with a Linux installed, most frameworks still assume CUDA and it's an effort to get them to use ROCm. For some tools all it takes is uninstalling PyTorch or Tensorflow and installing a special ROCm enabled version of those libraries. Sometimes it will be enough, sometimes it wasn't. Sometimes the project uses some auxiliary library like bitsandbytes which doesn't have an official ROCm fork, so you have to use unofficial ones (that you have to compile manually and Makefiles quickly get out of date). Which once again, may work or may not.
I have things set up for stable diffusion and text generation (oobabooga), and things mostly work, but sometimes they still don't. For example I can train stable diffusion embeddings and dreambooth checkpoints, but for some reason it crashes when I attempt to train a LORA. And I don't have enough expertise to debug it myself.
For things like video encoding most tools also assume CUDA will be present so you're stuck with CPU encoding which takes forever. If you're lucky, some tools may have a DirectML backend, which kinda works under Windows for AMD, but it's performance is usually far behind a ROCm implementation.