That's some kind of relativist argument I don't understand. Modelling and theory is an important part of science. We have something that is difficult to measure independently, so we build models to derive an explanation from things we can measure. And they did that. And the results line up with the hypothesis.

I mean, duh. Usually hypotheses are right! You're right that it would be more interesting if it showed some kind of confounding effect or whatever.

But it didn't. It turns out that the boring explanation seems like the right one: the anomalously high number of people who died of unexplained reasons in 2020 was just the giant global pandemic. Oh well.