I mean, the launcher part of the argument hardly matters anyway. Launchers aren't required to sell games. Its the storefront that matters, but in terms of having an online software store, Valve isn't even that dominant. Even limitting it to just selling games on Windows, while yes, Steam is the go-to, Microsoft (or prehaps more significantly Mojang), Riot games, Blizzard, and Roblox are all massive games that have their own stores (and launchers for that matter). There are also numerous other smaller games with their own pages, and more generalized storefronts that don't require the use of Valve's storefront or launcher such as Itch.io, Humble (they don't just sell Steam Keys), and GOG.