L4D2’s port was great when I played it, and Valve even made a big triumphant blog post with all the benchmarks proving it worked better than the Windows binary. Maybe your confusing it with Dying Light? That native port was so incredibly trash that everyone forced Proton on to avoid it.

Not really. Default drivers should work just fine. If you want to make sure they’re installed and running, run the following in a terminal:

glxinfo | grep Mesa

If you have any output, you have Mesa. It’ll tell you what version you have as well.