If that was an ideal strategy they would have never opened it up to publishers in the first place.
Google no doubt optimizes their algorithms for profit, but they surely don't need to block out publishers to ensure their own sites have ads to display.
Ad inventory supply is and always will be > demand. As such, their actions to make short-term revenue by banning publishers makes sense. It's basically recycling publishers, knowing the pubs wont be able to do anything about it. Obviously it hurts their brand but they're too big to give a shit.
Google no doubt optimizes their algorithms for profit, but they surely don't need to block out publishers to ensure their own sites have ads to display.