In Whitewater, the original investigation by Fiske quickly cleared the Clinton's, but the GOP reinstated the independent counsel law, which impaneled three Reagan conservatives, who fired Fiske because he was too moderate, and gave the investigation over to Starr, and that's when the games began -- a true witch-hunt.
There was basically no way for Reno to dismiss Starr at that point, as the Reagan appointed judges would have overruled her. Starr was then allowed to expand his jurisdiction into matters FAR removed from Whitewater, that included conspiracies about the Travel office, Vince Fosters suicide, the handling of FBI files in the WH, and finally the Jones civil suit.
It was basically an out in the open, political coup by Republicans.
Compare this to Mueller, who has indicted people for wire fraud, corrupt foreign lobbying, identity theft, election conspiracy, money laundering, and obstruction of justice. He isn't going after petty civil matters like Stormy Daniels, or Trump's other possible illegal behavior, he's focusing on corruption and foreign money alone.
The probes are night and day.