I have heard that it was very comprehensive and put the Mafiosi at a disadvantage they would never see again in Italy after his overthrow, but that felt rather propagandistic to me. Can I have a more measured view of this? Was the supposed cleanup just as fake or exaggerated as Hitler's reinvigoration of the German economy?
While you wait for new answers take a look at this one from /u/poopchen
I copy here an exhaustive reply by Fabiano Fava, an Italian blogger-historian specialized on the period before and during the Second World War. On his Facebook group "Seconda guerra mondiale 1939-1945" you can find many more of his very detailed posts (in Italian), all complete with sources.
'The famous 'iron prefect' Cesare Mori sent to Sicily to solve the Mafia problem on behalf of PNF - Partito Nazionale Fascista (National Fascist Party) succeeded in arresting a great many low-ranking exponents and striking a few godfathers but, summarising some related texts and essays: <<But soon, political-business circles of the fascist area colluded with the mafia managed to direct, with dossier activity, the investigations of Mori and the Attorney General Luigi Giampietro on the radical wing of Sicilian fascism, also involving the federal and PNF deputy Alfredo Cucco, one of the leading exponents of the fascist party on the island. Cucco in 1927 was even expelled from the PNF and the Chamber 'for moral indignity', and put on trial on charges of having received money and favours from the Mafia, being first convicted but then acquitted on appeal four years later. But, in the meantime, the Sicilian fascist party was decapitated of its radical elements. Only that these extirpated 'radical elements' belonged to that 'violent' or 'extremist' wing of the PNF that Mussolini intended to remove from positions of power, in the course of his policy of 'institutionalisation, moderation' of the various internal currents of fascism. The elimination of Cucco from the political life of the island favoured the installation, in the Sicilian PNF, of the island's latifundists, often themselves already colluding with or at least contiguous to the Mafia, but belonging to that internal current, of fascism, which well appreciated Mussolini's governmental turn and agreed with the elimination, or at least the downsizing, of the various revolutionary fringes, no longer necessary>>.
In practice, therefore, Mori was left free to act only as long as he hit elements that Fascism intended to expel. And he was 'wisely' directed towards a specific part (the expendable part) of the party officials. Not for this reason his action was a failure, it must be said: many Mafia families were almost annihilated, some bosses had to find refuge with their American friends/relatives, and indeed the Mafia had a hard time during the few months of Mori's operation.
But as soon as he came into contact with elements that the regime instead wanted to save (because they were well suited to the new 'institutional' image that the party had to assume as soon as possible), the 'iron prefect' was the object of the most classic and striking promoveatur ut amoveatur: promoted so that he could be removed, recalled to Rome for other tasks 😉
Sources for this foreword:
Translated with www.DeepL.com/Translator (free version)