There's some value in having open-source clients to proprietary services. Of course ideally one would avoid using them, but since many are stuck with games they already purchased and the launcher was bolted on later in an update, it makes sense.

At the very least it probably doesn't implement a lot of the telemetry, and it doesn't require you to figure out how to make the launcher work under Proton, only the game.

Less proprietary is better than nothing.