Source is this video:
Windows Was The Problem All Along - Dave2D
We could obviously compare performance between windows and steamOS before on the steam deck, or between windows and Bazzite on other handhelds. But this is the first time we have had official windows and SteamOS builds for the same hardware.
Proton uses Wine, which is a Windows system call API translation layer for Linux. In other words, it translates commands for the Windows kernel into calls for the Linux kernel.
So it’s kind of an emulator and kind of not, but regardless the metaphor of a translator is fine. As a lightweight translator, you might say it’s like using Google Translate on your phone to translate back and forth quickly and automatically, rather than having a person in the middle who needs to think about it.
In Software Design terminology, Wine and DXVK are “adaptor” layers (each convert one kind of API interface into a different kind - Wine doing Windows API to Linux API conversion and DXVK doing DirectX API to Vulkan API - and nothing more) whilst Proton is more a controller that just manages those things and adds some more functionality on top such as Steam integration for ease of use.
Without Proton users would have to know a bunch of command lines parameters and environment setup to launch all the right components with the right configuration so that they can first install and then run their Windows game in Linux. In fact this is the situation if you use Wine directly without something like Lutris to do a similar work as Proton.
Personally I prefer Lutris since it’s more flexible - for example I can configure it to run games sandboxed with networking disabled - and it’s not tightly bound to a single games store.
I used to use Lutris, but I found Heroic more consistent and convenient for filling the same purpose. It’s quite good at downloading just the diff needed for GoG game updates these days, for instance, which is key for big games like Baldur’s Gate 3.
I’d say it’s something like a babelfish. You speak English, I hear Spanish.