If, hypothetically, you have identified a strain that has had no severe outcomes even in a large cohort of people with known risk factors, then that strain is most likely harmless.
Of course we don't have this kind of data (yet), but the principle is valid.
This is why it is a good idea to read the entire post before commenting. The process of checking each candidate strain requires going into the local community where the index case was found and looking for more cases.
If, hypothetically, you have identified a strain that has had no severe outcomes even in a large cohort of people with known risk factors, then that strain is most likely harmless.
Of course we don't have this kind of data (yet), but the principle is valid.