Vulkan is fundamentally broken (
stutters & bad frametimes). But DX12 is smooth and just a tiny bit worse than Vulkan. So it's annoying but not the end of the world.
Most people are complaining because the game is badly optimized. Hard to judge currently, we'd need to know what settings consoles are using and compare performance with PC hardware that is relatively similar to consoles.
All I can say is: Certain Forums and PC crowds are dying over ULTRA settings. Having the latest and best hardware doesn't give you a free ticket to max out everything.
Ultra, but turning down Water physics to 50% alone is giving me +40% performance when there is a small river or even a tiny stream in the scene.
Further turning down from ULTRA to HIGH gives me another +30% performance on average (with advanced features still set to on) for example.
But than there are some people who aren't able to even start the game because the Rockstar Launcher is crashing. Most people are blaming Ryzen CPUs, but there are enough Intel reports too. Personally I'm also on Ryzen 3000 and the Client isn't crashing for me. Hard to tell what's the problem here, outdated Windows? it seems to be the Anti Virus sometimes, Rockstar is saying that you need the newest drivers etc.