I understand there's a pretty solid consensus that it did. In some places, serfdom effectively ended. But we don't have to guess. We can just look it up and find that people who know a lot more about it than us have come to those conclusions.
I think you misunderstood my previous comment. I don't at all question that the Black Death ended serfdom, or at least weakened it severely after so many dead. As I stated, I was questioning the application of this same chain of events and logic to the 1918 pandemic, for the population proportion reasons I already mentioned above.