Your 91% conviction rate only exists because of vetting DOJ investigations that are NOT indicted or charged via pre-indictment pleas.
For the clueless, cases are brought to federal prosecutors for investigation and consideration for federal charges. At least half are not charged or indicted because the DOJ (prior to this Administration) had protocols and ethical guidelines in place to ensure that they only went forward on cases where evidence for conviction was clear, and there were no issues that would taint the integrity of the prosecution. DOJ investigations often take months or years.
Then came Trump. And Bondi.
And yes Ned. I know how Grand Juries work.