kohlrak: If vsync were the issue, you should have the exact opposite problem: cursor should be the only thing that doesn't lag, or they should lag equally.
eric5h5: Not necessarily; lag on a cursor can be much easier to see compared to moving the camera around. If the game uses a software cursor, then it must update at the same rate as the game, whereas a hardware cursor is independent and will always update at the screen refresh rate. You can see the difference in the attached gifs, where the software cursor (block) keeps up with the hardware cursor (arrow) without vsync, but visibly lags with vsync.
I personally absolutely can't tell one frame of lag when playing a FPS game, so I always use vsync. If garbage drivers or vsync implementation bugs are somehow adding multiple frames, then yeah, that would be a problem. But I can usually tell when the devs are using a software cursor.
That's not input lag, though, but output lag. This is demonstrated by the "hardware cursor" keeping up. And, in light of my recent discovery, I have to ask what APi was used to produce that? SDL? DX? OpenGL? It's starting to look like an issue with Microsoft in particular attempting to create a long back-buffer to present frame stability which, in turn, results in output delays of several frames. Nice to see someone trying with the "hardware cursor," though as this means if i used FFMPEG i could easily find the exact delay.
EDIT: Vsync has 2 frames of output delay, and the visuals are clearly exacerbated by the input sampling rate. WIthout vsync, there's still a 1 frame delay.
I do find it curious that the dramatic back and forth movements are not replecated with the non-vsync version.
EDIT again: novsync has 1 or 2 frames of delay, vsync version has 4 frames of delay. Just caught that the recording is at 30fps unlike the output of the program.
Final edit: i'm gonna guess that the lack of tearing during all this demonstrates that there is some vsync going on at another abstraction layer, too. At over 500fps, i should not be seeing that delay, yet i am.