I am really puzzled by the negative sentiment around adtech on Hacker News, especially since I would guess that a lot of people here have a salary that depends directly or indirectly on advertising. "Tracking" gets a lot of bad press, so much so that I sometimes wonder if this is not organized by the tech giants (Apple, Google, Facebook) who have access to their own first party and who thus have much less to lose when cross site tracking disappears. Adtech providers only have access to products you buy/see, for a limited time and without any personal data, meanwhile Google and Facebook know everything about you, your friends, your center of interests the places you go to, along with your name but somehow everyone seems hell-bent on abolishing 3rd-party cookies. Apple's own apps are not subject to this change, and as noted by other commenters this will probably shift budgets to subscription of which Apple takes its cut. All this will further the supremacy of walled-gardens and big tech, at the expense of smaller independent players.
I'll be honest, there is a creepy feeling when being tracked cross-site, and adtech providers have collectively failed at providing explanations, and a transparent account of how this works and why this is useful. They have also relied on fingerprinting, which has hurt the credibility of the field. The issue is that the replacement that are currently in the works (https://github.com/WICG/floc and https://github.com/WICG/turtledove/blob/main/FLEDGE.md) are extremely complex, will still dramatically impact adtech performance and only improve privacy for a very contrived definition of the concept which incidentally benefits once again big tech vendors...
As to the effectiveness of advertising, removing tracking will have a huge impact. And this affects all players in the value chain, not only adtech providers but also publishers and more importantly advertisers which will see their return on ad spent severely impacted. There is a real of loss "social welfare" (I mean in a game-theoretic sense, but also for real if you believe in capitalism) if tracking is disabled. The freakonomics article gets cited a lot but the industry as a whole is moving forward with a greater emphasis on proving incremental sales. Advanced clients (who can spend billions per year) have real statisticians doing permanent randomized control trials proving that every dollar spent is providing incremental sales. I work for an adtech company and we have automatic RCTs for every single client, and guess what, advertising works for most clients. This is on top of fact that we are measuring the effectiveness of dollars spent on us, in addition to the dollars spent on competitors/other channels on which we have no control of course. The fact that Uber could see no impact when going from 150m to 50m is a testament to the incompetency of their CMO, which could not be bothered to actually measure and pilot the campaigns correctly, not the effectiveness of adtech as a whole. Thoughts are my own not my employer's.