Your "hack" wouldn't work. The first company would still have to validate that their tests were accurately detecting SNPs. Then the second company would still have to validate that their "diagnoses" were accurate. Medical devices aren't restricted to physical tests. If it is used in the diagnosis of disease, even if it is just software, then it still might be a medical device. This is especially true if it is marketed directly to the consumer.

23andMe does more than just create hyperlinks between genes and research papers. It tries to assign risk.

History has shown that a little regulation in this field is a good thing (and just might make the 23andMe product better).