Non-random samples get you to up to 10% fatality rate. I have the data for my region and in march-april 2020 the IFR was 10-15%. Of course, that was due because there weren't enough tests and only the ones that were really sick entered the statistics. But for the original strain, IFR was around 1% and that number was pretty consistent among a broad number of studies.
Also, take into account the amount of diseases that are getting late treatments due to healthcare saturation. I don't know of any formal studies but you only need to talk with any doctor to see that they're consistently seeing diseases in later stages and therefore harder to cure.
