That's not how it plays out though. More effective/profitable ads does not lead to less ads being shown. In fact, it's the opposite. As ads have become more targeted, and theoretically more profitable according to this argument, we have more of them.
There is no set "amount of effectiveness," so to speak. If ads are more profitable, advertisers are still going to spend just as much or more on them, precisely because they have a higher ROI.
There is no set "amount of effectiveness," so to speak. If ads are more profitable, advertisers are still going to spend just as much or more on them, precisely because they have a higher ROI.