MarkoH01: No, it's not. That would only be the case if you are actually USING Galaxy. Since Galaxy should be completely OPTIONAL the fact that Galaxy does do the exact same thing (which ist does not because it downloads other files) does not make GOG downloader redundant. If I don't want to use Galaxy (because it's buggy as hell, costs performance and does not work the way it should) I need GOG downloader.
First of all, you can download the exact same installer files with the Galaxy client as you do with either the browser or the old GOG Downloader client, the ones that don't need Galaxy at all for either installing nor running the games. That part of Galaxy does indeed make the GOG Downloader client redundant.
There is also the option in Galaxy to not to separately download the installers, but just download+install the game, Steam-like. You don't have to use this feature, you can use Galaxy as only an installer downloader.
Your argument that "Galaxy is not optional because then I don't have an option to use GOG Downloader client, and I don't want to use the browser download links either" is a bit silly because it would similarly mean that the old GOG Downloader client wasn't optional either. If you didn't want to use the browser links before, then your only option indeed was to use the GOG Downloader, I guess. So all this time, GOG required a client, even before Galaxy???
I personally don't understand in general why people, who were always fine using the GOG Downloader client to download their GOG installers, would refuse to use another client (Galaxy) for exactly the same purpose. Ok there is one drawback for me with Galaxy, it seems more finicky about the internet connection (ie. I can't download my games with it at my workplace, something that was possible with GOG Downloader; maybe using blocked ports or something).