I can’t really speak to the performance of your system and I have only played the Witcher 3 and Valheim (birefly) out of those games. The Witcher 3 ran great on a core i5 3570k and gtx 1060 about 2 years ago, and Valheim I ran briefly on a ryzen 3600 and radeon 5700xt, without any performance issues.
Since you are on Arch, I assume you are running a recent kernel and recent mesa already, so I would suggest looking at protondb.com or lutris.org for any hints at some wine/proton configurations you could use.
You might also try disabling/enabling esync (and/or fsync), try different versions of wine (in lutris) or proton, The Witcher for example was already running great on wine/proton 4.something already, so could be there are some regressions on later versions.
You can also try lowering your settings in games and turning off non-essential graphics features like tessalation or others that may or may not have different performance impact on your system on linux vs. windows.
Also, are you running an X or Wayland session? 
Yes I had set the anti aliasing and sharpening settings the same. I even just tried cranking all visual settings to max including anti aliasing and it still doesn’t look as good as it does on Windows for some reason.
I am running the most recent kernel. I did look on protondb’s website and a lot of what I was seeing was people saying it either worked great out of the box, that it needed to be run for about 10 minutes to load in all the resources, or that they had lots of issues and generally saying it didn’t work. I didn’t even think about disabling esync, fsync, or disabling freesync on my monitor. I will try that. Same thing for trying different versions of Wine in Lutris. I did try different version of proton and it didn’t impact performance in any way that I could tell. Also, I am running an X session. I’m using KDE Plasma for my desktop environment, as I don’t care for gnome, and XFCE has issues with my dual monitor setup.