Did you try the NVidia driver from the Debian repo and/or NVidia themselves? The former would not load on my Optimus machines either, without any clue as to why. (I sunk more time than I should've into this. I literally tried everything on the wiki pages to discover they are horribly outdated.) I totally agree: this is not great. I know people will blame me for choosing NVidia, or NVidia, but why can Fedora, Ubuntu et al do this right?