Well yes... I was responding to your question about why a launcher would need HDR support.
It needs HDR support because "steam" is more than just a launcher. It includes proton, which needs HDR support so that games that have HDR support can use HDR.
Not really. Steam doesn't include Proton by default. It's downloaded on demand. It's a separate product with its own code base (derived from WINE), bug tracker, and since recently even its own logo.
Just because it's an optional component, doesn't mean that it isn't part of an overarching product. KDE contains many different parts that may or may not be installed, that doesn't mean they aren't part of KDE. "Steam" is a larger product composed of separate models such as the GUI and compatibility layer.
That’s just the client itself. It’s also not entirely their fault, since they use CEF, and CEF is a colossal pain in the ass. The issues and the pull requests are all there, but it doesn’t seem like anyone is actively working on them at this point
Last I saw it was about merging in the upstream CEF wayland support
but yes, the client could be x11 and somehow still launch games in wayland, which could also be a solution - not too dissimilar to gamescope I suppose. I ain't got no clue on how that works tho ¯\_(ツ)_/¯