During Ask Us Anything, id Software revealed that Quake Champions will indeed come to Steam. Currently, the latest instalment in the classic shooter series is available only through Bethesda Launcher.
Quake Champions Will Release On Steam
You will still be required to have a linked Bethesda.net account, but users playing the game from Steam will not go through the Bethesda.net launcher. During the current beta period the game will only be available through the Bethesda.net launcher.
No other information is currently known, including the possible release date of the project. You can read the full text of AMA following the link above.