Both offer you licenses, but the offline installers are going to work even after a license has been revoked. And yes, this is a HUGE difference for the gamer. Unless Epic and Valve now enforce the swatting of GOG customers' homes after licenses have been revoked to delete/destroy the offline installers.
Just like movies/series on discs, offline game installers are a nightmare for the entertainment industry and censorship-happy groups and parties.
In the current political and social climate,
don't be an aggressive monkey . Show that you have evolved that important thin sugar coating called civilization. Don't fall for the fools.