VSYNC only applies when in true full screen mode. So long as you are running in a window (bordered or borderless modes), the game engine should try to run as high as the in-game configuration allows it (no FPS cap set, it should try to render as if there was no v-sync). So, if you want to choke it off at your monitor's refresh rate while in borderless/bordered modes you would need to set it to 1:1 FPS cap and then make sure the config file has the proper refresh rate (may require a manual edit of FFXIV.CFG to the proper refreshrate after you set the FPS cap in the GUI).