It wasn’t that long ago that the scientists were suggesting 70% was sufficient. Is it that >90% is required when the vaccines don’t effectively impede transmission? Is it possible 100% would not be sufficient?
Look at how prevalent pre-delta variants are now: no, they have not disappeared because almost everybody had delta, they have disappeared because of vaccine shots combined with moderate (compared to 2020) NPI. A virus strain does not simply disappear because there's a new one in town, it keeps replicating until it runs out of hosts. And virions are certainly not defecting to a newer, more glorious flag (like humans might do)