In the end click-to-photon latency is what matters, so measuring the whole system end to end is good starting point, and that means video camera pointing at screen. Something like wf-recoder sees only part of the whole pipeline. How much latency is there between compositor copying frame to wf-recorder and same frame getting pushed physically out on the display cable? Without knowing exactly how the whole system is built such question is difficult to answer.
But you also have to account for the fact that wf-recorder might interfere with the results, capturing screen is not free, and it might even push some part of the pipeline to less optimal paths. With video camera you can be fairly confident that measuring isn't interfering with anything.
Mhm makes sense, maybe something like a capture card with a high refresh rate would be the best option, as it won't interfere with the OS, and eliminates the delay between your camera capturing a frame and your monitor refresh rate.
Sure high-speed capture card could be nice. But when many smartphones can do high-speed video, some even 960 fps, then that is very convenient (and low-cost) solution.
But you also have to account for the fact that wf-recorder might interfere with the results, capturing screen is not free, and it might even push some part of the pipeline to less optimal paths. With video camera you can be fairly confident that measuring isn't interfering with anything.