@mitu well I installed Steam through pi-apps, and I believe it installs box64 with Steam but when I was testing my theory I installed it for good measure together with wine and box86. Shotgun approach and all that, and I need wine for OpenBor and Mugen games.
But what initally happened was that if I installed Steam after RetroPie, Steam wouldn't finish the last installation step, when it asks to install a bunch of dependencies and then fails. So when I install Steam before Retropie, comment out the contents of sdl1.sh, sdl2.sh, and sdl12-compat.sh, (making sure all dependencies are met) and install RetroPie, it seems to use the system's sdl libraries to build things. So far everything's working as expected. Yeah, I see what you mean about using a translation layer. I'm ok with that. I can play TMNT Shredder's Revenge and a few others just fine.
Yeah, had no issues with Steamlink. Installed it and it worked right out of the box which is nice to have for games unwilling to run locally!