My time is actually more valuable than this. There are signals available to them to show they take original work seriously and are bucking their cultural trends of cheating academia to get worthless degrees.
The opt-out, is to navigate away and not use their service. Which matches the GDPR - if you need the data to create a contract - like 'we use your data in exchange for your use of our site' then you can keep it.
> there’s not a lawful basis unless advertising-cookies are suddenly the enabling technology behind downloadable containers.
Yes they are. Advertising cookies are how those downloadable containers are provided. That's an enabling technology. It wouldn't exist otherwise in the technology ghetto of the EU.