If the investigation was fraudulent, any person accused of a procedural crime should be removed. Without the investigation, mo-one would have been interviewed and would never have told lies to anyone.
That would let Stone, Flynn, Papadopoulos go. If the Ukrainian "Black Dossier" was a fabrication, as is now suspected, then Manafort should not have been convicted either.
What was wrong with Mueller's investigation? It was based on information obtained from electronic surveillance conducted by intelligence agencies in the United States. That surveillance was allowed due to FISA arrest warrants obtained by the Steele Dossier. That dossier is also believed to be a manufacture.
In fact, the head of Fusion GPS, Glenn Simpson, wrote a very similar document some years earlier. It's almost as if it was recycled for use against Trump.
If FISA detention orders did not have a solid legal basis, the information collected as a result cannot be used in court. Mueller knew that Steele Dossier was not reliable or verified as soon as he assumed the position of Special Advisor.