Larian games have been DRM free since Divinity 2 Developer's Cut, a DRM free patch was released for the earlier Divinity 2 Dragon Knight Saga release and some Beyond Divinity retail releases, and the digital releases of Divine Divinity and Beyond Divinity are DRM free (the last retail Divine Divinity update removed the DRM, though the game still requires the disk to play a couple of cutscene videos).
Updates through Galaxy are generally available at the same time as Steam. GOG's patches and updates to the full installers are usually ready within one or two business days.
The timing of Galaxy updates are dependent on the developer; GOG handles the patches and full installers.
Thanks for the reply, that clarifies everything I need to know to make a choice (and hopefully for other people posting here too).
I'm not bothered by most DRM, only by a few ones that are too aggressive, but I certainly appreciate the companies proposing DRM-free options to their customers!
