This is how it has worked for ages. If you think about it for a bit, I think you'd come up with all kinds of reasons for why this can't be done with just server-side signals.

For example, how do you account for skipping over already fetched parts of the video or rewatching the same section multiple times?

Or for the entire video being cached and researched? For bots downloading the video?

The idea that this is some malicious anti-adblocker time bomb implanted a decade ago is preposterous.