Well...according to devs, separated the launcher from the game helps devs focus on the game itself.
(Yah CK2 is near its EoL but it's still buggy as hell. I've rolled back to relatively stable 3.2.1.0 with tons of handmade-dirty fixes.)
People hate it somehow because it breaks mod loading, the main function of a launcher.
If the new launcher using contemporary Steam workshop API to manage mods, rather than current legacy, obsolete API, I'd endure the temporary inconvenience.
But if the new launcher is yet another advertising/promoting platform...I'd said fxxk u.