Once the rewritten "amdgpu" driver came out, things got much better. The first few cards created after that (IIRC the Polaris GPUs, RX 400's), the situation reversed. I still have had occasional issues with various Nvidia cards (normally driver updates breaking things), but for almost a decade now, I have not had issues with AMD GPUs under Linux.
[0] Except for pro features while using workstation cards. You need to use a proprietary driver for those, but even those share a lot of code with the open source driver.
I forgot that name "fglrx", probably a mental self-defense mechanism. Those were some bad times, trying to get different display outputs to work at the same time, guessing and testing values in xorg.conf, so on. There was some community utility someone wrote to try and help with installation, reinstallation, configuration and reconfiguration, but the name eludes me now.
I would edit my post to correct it, but it seems the edit window has passed.