I am currently running GTA V from Heroic with Proton GE Latest.
I have Fsync, Esync and Gamemode enabled. When it runs on windows, GTA V gets around 115 FPS and GTA O gets around 60-70 whilst on Linux
GTA V gets around 80 FPS and GTA O gets a mere 30 FPS.
Review on the ProtonDB says GTA runs as good as native, yet in this case it's the contrary that's been happening, Any help is appreciated greatly :)
PS: I got all my drivers up to date, and my fs is ext4
GTAV works better with AMDVLK, as one of the very few games out there. You could give that a shot, but be aware that AMDVLK often gets selected as default, so having AMD_VULKAN_ICD=RADV in your global Env. Variables are a good idea.
And then launching GTAV with AMD_VULKAN_ICD=AMDVLK %command%.