You misinterpreted the NIH numbers. It isn't 57% of 400 are untreated, but rather 57% of ~90 (NIH state 1 in 6/ 22.8% love with AMI). In any case though that ~90 figure relates to AMI which is a broad definition and includes very mild cases, whereas my numbers were related to SMI - which tends to be 5% (as supported by your NIH source). Having worked in the field, untreated schizophrenia is a lot more serious than untreated GAD or ADHD.

Edit: my gunshot source: https://www.pewresearch.org/short-reads/2023/04/26/what-the-data-says-about-gun-deaths-in-the-u-s/

Funnilly enough, if 2 people were shot a day in OP's scenario, one of those would statistically be a suicide.