I don't understand your easy dismissal of this kind of prosecutor activity. It's not like there was a trial and lying was the only charge they could make stick.
It's not "He murdered those 4 coeds but at least we caught him lying about it." It's "We showed him we could take him down hard for the bank heist, and in exchange for leniency he helped us take down the whole Mafia."
Obviously we don't yet know the degree to which Papadoofus is aiding the investigation because the investigation is ongoing and locked up tight. But historically, flipping small fish through plea deals is the way conspiracies are busted. It's what happens.
(I haven't read everything Mr. Fed has written on plea bargains, but I seem to recall that he has focused on prosecutors pressuring guilty pleas out of poorly-educated or poorly-defended suspects simply to keep the machinery of justice humming and to boost their own scores. There's no question of "cooperation agreements" in such cases because the suspect has nothing to offer.)