I must be missing something. Isn't GSync just a fancy version of vsync for variable framerate? And shouldn't your monitor fall back to standard vysnc when your FPS drops to 30? I can see the issue if you can hit the 40s and GSync can't go that low (in my case I just set refresh to 144 and vsync at 48), but otherwise I'm still confused why 30 fps is a problem... Perhaps this GSync isn't what I thought it was - I'll happily accept education if I'm wrong.
VSync prevents tearing by locking FPS below the threshold of your monitor's max refresh rate. So at 60Hz, VSync locks the game to 60FPS (and adds some input lag). VRR is the general term for variable framerate, and on PC comes via Freesync (AMD) and GSync (NVidia). With HDMI 2.1 you also have the default VRR consoles most likely use (and which is pretty much identical to Freesync).
What VRR does is match the refresh rate of the monitor to the output of the app. So a 60Hz monitor goes down to 45 if I only get 45FPS. But I cant go below 40Hz, that is a hardware limitation of the monitor. What LFC does is double the framerate so it falls back into the range of the monitor: a 24FPS becomes 48FPS, which is back into VRR range.
The advantages are significantly reduced when you have a nearly perfect locked FPS at something your monitor's native refresh rate is a multiple off, but it is still an advantage.