Steam Link is always going to be better wired. Everytime.
I used to live across from a building that was concave. I could literally see about 100 Wi-Fi networks because of it and I never had issues with my AppleTv or anything wireless for that matter. I’d try changing channels first to see if that helps.
The higher the GHZ, the less it penetrates walls. So depending on where the AP and the Apple TV are will start mattering more.
Because you don’t use FindMy for the remote control.