There were people saying right at the time in 2020 that the 1% IFR was nonsense and far too high. It wasn't something that only became visible in hindsight.

Epidemiology tends to conflate IFR and CFR, that's one of the issues Ioannidis was highlighting in his work. IFR estimates do decline over time but they decline even in the absence of natural immunity buildup, because doctors start becoming aware of more mild cases where the patient recovered without being detected. That leads to a higher number of infections with the same number of fatalities, hence lower IFR computed even retroactively, but there's no biological change happening. It's just a case of data collection limits.

That problem is what motivated the serosurvey. A theoretically perfect serosurvey doesn't have such issues. So, one would expect it to calculate a lower IFR and be a valuable type of study to do well. Part of the background of that work and why it was controversial is large parts of the public health community didn't actually want to know the true IFR because they knew it would be much lower than their initial back-of-the-envelope calculations based on e.g. news reports from China. Surveys like that should have been commissioned by governments at scale, with enough data to resolve any possible complaint, but weren't because public health bodies are just not incentivized that way. Ioannidis didn't play ball and the pro lockdown camp gave him a public beating. I think he was much closer to reality than they were, though. The whole saga spoke to the very warped incentives that come into play the moment you put the word "public" in front of something.