Here's a brief overview of the major studies...
The claim that medical errors are the third leading cause of death in the US has always rested on very shaky evidence; yet it's become common wisdom that is cited as though everyone accepts it. But if
sciencebasedmedicine.org
Secondly, when discussing errors in the oft-cited Hopkins stat (that is the third leading cause of death news following the IOM numbers 20 years ago) the intent was to highlight SYSTEMIC errors that include fractured care. Someone gives a med. Someone else gives a med. Neither is aware of the other doctor. The patient doesn't tell either. Patient takes both meds and exacerbates their heart failure. They die. That's an error. That isn't negligence. It's a systemic problem. In the Hopkins study they were only looking at inpatient errors that could include medical reconciliation missing home meds or the patient providing old bottles because they don't know better, leading to a doctor not know what the patient was taking and a bad medication usage. That's not negligence. It is an error that should be prevented.
1> We don't have that many systemic errors (as the number you cite). But we do have a shit load that need to be fixed.
2> The vast majority of errors are due to things like the above because our healthcare system, especially around records sharing and communication with nursing is absolute garbage.
3> There is too much variation in the US system and this allows a swiss cheese model where these errors are produced at abnormally high rates because they are hard to spot without such consistency.