The problem is the chain of custody. If they’d raided Hunter’s home and seized the computer, that’s one thing, but a copy of a hard disk that has passed through several hands...any prosecutor is going to be wary of bringing that to court. The shape of the argument to throw it out is already out there—it comes from people with a political agenda, Russian disinformation, etc. And if the prosecutor doesn’t want to bring charges based on that evidence, the cops aren’t going to waste their time.
The FBI has the original Hard drive. Could a prosecutor get it from the FBI?