You were arguing that the infection rate has "come back down" (i.e., trended downwards); that's the central claim about Sweden used to support your hypothesis in post #465 which sparked this whole discussion.Correct. It does not tell you about trajectory. It tells you about scale. Tests, death rate, hospitalizations, etc. Those do an alright job with plotting trajectory when done consistently (which they didn't do the tests in Sweden consistently, so deaths and hospitalizations are better proxy variables for trajectory there). You do serology studies to establish scale. When the question is "what percentage of people have been infected and recovered", that isn't a question of trajectory, that is a question of scale.
And the whole reason antibody tests were brought up in the first place was that you disputed the usefulness of positivity rate when I showed that it doesn't support the idea of a downward trend. So now, when I make the argument that antibody tests are an even worse metric for studying trends, suddenly it's not about trends at all? Trends are what you were initially talking about! The supposed trend was your supportive evidence!