But I don't want to have another launcher open in the background.

You actually won't need to have the launcher open in the background or even be signed in or anything.

Satisfactory can be played offline, and if that's the case, you won't need the launcher open.

But if you want to use any online features, like to play multiplayer, then yeah, you need to have the launcher open and signed in and whatnot.

The alpha at the moment is a closed alpha and so therefore for now the launcher is required but in the future it won't be required.