I may not like it, but you do make an interesting technical argument.
I think it would still be detectable though because of buffering.
What you're saying assumes that videos are streamed frame-by-frame: "here's a frame", "okay, I watched that frame", "okay, here's the next frame".
With buffering videos will preload the next 30 seconds of video, and so if you pressed a button to skip ahead 10 seconds, that often happens instantly because the computer has already stored the next 30 seconds of video. Your plan to just pretend to skip ahead doesn't work in this case, because my computer can know whether or not it really did skip ahead, because of buffering.