The Launcher is just a fancy (and bloated*) front-end for writing a small JSON file: Documents > Paradox Interactive > Hearts of Iron IV > dlc_load.json, that is then read by HOI 4 when it starts.
Tip: You can use the Launcher whenever you need to create/delete playsets, add/remove mods, enable/disable mods in playsets, or enable/disable DLCs, that is not very often, and bypass it otherwise, that is most of the time. To bypass it, don't click the 'Play' button in Steam, instead open the hoi4.exe program file directly in Steam > steamapps > common > Hearts of Iron IV. You can make a shortcut to hoi4.exe in Windows Explorer and put it on your desktop, for example, for more convenient access. If the Steam client is already running in the background, all Steam features will work.
If you're feeling 'hard-core' you could even change the set of mods used by directly editing the dlc_load.json file with a text editor, before opening hoi4.exe. But I wouldn't recommend it.
The same trick can be used with EU 4 and Stellaris, and probably with CK 3 too.
(*) It's basically a whole embedded Chrome web browser + some more stuff.