Wow. This is a good question beyond my salary grade. But I can answer your question about removing DNA from genealogy databases from a practical standpoint.
First, just because one person chooses to remove their DNA doesn’t prevent hundreds of other distant relatives out there from triangulating. We still use this technique to find a person anyway.
In the US, what happened next was that the identity was not actually used as evidence. It is only used by the police to gather traditional evidence to convict. So, in the case of the Golden State Killer, he was first identified using the technology that found the Somerton man.
Police then tracked him down, and the evidence convicting him was traditional DNA from a paper cup the man had thrown in the street. That DNA is then matched to DNA at the crime scene. So if one of his distant relatives removed their DNA genealogy data from the site, that would have absolutely no effect on the results.
Police will still convict based on traditional evidence.