Proton too just automates the work that somebody did in the form of install instructions, same as Lutris.
The difference is that those making the install scripts for Proton are paid for and you don't get the option to fix them or make your own, which means that there are in fact fewer games with Steam install instructions (i.e. Steam Support) than games with Lutris install scripts.
Further, there are fewer things you can tweak in Proton and they're all either changing the proton version or some badly documented text parameters that get fed to its command line, whilst Lutris actually has most such options in menus: the learning curve for just starting a game is lower in Steam that in Lutris when it works but the learning curve for fixing it when it does not work is lower in Lutris and sometimes you simply don't have access to change what's needed to fix it in Steam but you do in Lutris.
If you use Lutris with its GoG integration the experience is generally the same kind of Click & Play as Proton of Steam and whilst the rate of problems seems to still be a bit bigger in Lutris, surprisingly (at least for me) it's not by much.
For me in Lutris having to go and install Microsoft components using Winetricks is generally only needed for some standalone installer executables, not when using GoG integration.
Steam is great when it works and a massive headache and pretty limited on what you can do when it doesn't, whilst at least with GoG integration Lutris is great when it works and still a headache when it doesn't but not as much as Steam and it gives you a lot more options to try and get it to work, plus the coverage of pre-made installer scripts in Lutris (which is what makes games "just work" in it) seems to be broader than in Steam, including covering older and more obscure titles, plus that coverage is probably growing faster because the scripts are user contributed rather than the work that can be done adding support being limited by how many people Valve (who are notorious for having very few employees for a company that size) hired to work on it.