Ok. So ideal perfect world vsync would introduce no extra input lag? So for every game where I've disabled it any noticed a difference (that's every game), those games weren't optimised ideally or the gpu isn't doing a perfect job or whatever for that to hold true. So perhaps one could say that vsync kinda sorta is causing that noticeable input lag in those games, and disabling it would be a good idea if you want to get good precision of movement.
Take note of what they do in VR.
They have Vsync enabled with a short render chain with Double Buffering. There is no way around it. Vsync ensures frames are written to the display when the display is ready for it thus also ensuring that complete frames hit the display with consistent timing. Double Buffering is the minimum output queue you want, because you don't want to write to the same buffer that the display is reading from.
What VR games do differently is they don't triple buffer or queue any frames, but then they *absolutely* cannot miss a frame in the rendering window because then you get a massive lag spike.
Lag is a consequence of buffering+vsync.