It absolutely is effective -- but there's economics at play. You can't 100% close the whole on anything. Scrappers can themselves employee expensive techniques to try to sort or clean content pre-training.
But altering the economics is meaningful, even if it won't give you strong guarantees. Big, maximalist systems fall from a million paper cuts. They live or die on the economics of the smaller parts.
It's the same story as has ever been. "Smart People"'s position on anything is often informed by their current economic relationship wrt to the things they care about. And maybe even Yud isn't super happy about his profession being co-opted. What scraps will he have if his own delusions became true about GPT zombies replacing "authentic voices"?
No one is immune to seeing a better take when it's their shit on the line, and no is immune from being in a bubble without stake.