Mussolini was totally insane by the time Hitler decided to partner with him. He was in the latter stages of syphilitic megalomania, a disease he first contracted as a young man. Like Goering, he simply could not tell the truth to Hitler. The 70 aircraft a month Italy was able to produce became 500 aircraft. The 500 aircraft he had in the Italian arsenal were reported to Hitler as over 5000. Italy did produce 11,508 combat aircraft during the Second World War. Of course his delusion was not shared by the actual Italian Air Force personnel. So to keep the validity of the illusion that there were in fact this many Italian combat aircraft, whole squadrons had to be flown and literally shifted from one airfield to the next as Hitler paraded around them inspecting his empire. On the ground Mussolini did not fare much better. He could not defeat ground forces anywhere in Africa, and no one beat up the Italians like the British.
The Italians had a perfunctory war machine and couldn’t get force levels up to snuff once the war began. Most of the weapons the Italian army used had already been used on the Ethiopians and the Eritreans. The Armato tank was a joke. Germans would take these Italian MBTs and turn them into ammunition vehicles, because all they were good for was carrying supplies. The Breda B88 medium bomber ground attack aircraft was introduced in the mid 1930s and this plane fared so poorly, most of them were used as decoys in decoy airstrips made to draw off enemy bombers.
The Italians who defended the Allied Invasion at Anzio fought very hard. It is a myth that they all surrendered. They honestly saw this as a foreign invasion on native soil and many Americans paid the price at the hands of these determined defenders. The fact is that Italians were unhappy with the widespread destruction of their country that was caused by Benito Mussolini. Italian insurgents had a big effect on the Allied win in Italy and worked hard to overthrow Il Duce.
Hitler had to send Afrika Korps to rescue Italian troops, sometimes in a rush so he could reverse a bad situation before the unmotivated Italian troops threw their hands up. By the middle of 1943, the British held over a million Italian prisoners. In fact when the Allies invaded and the Italian fascists lost control from Sicily to Montecasino, Hitler air lifted Benito and his girl Clara Petacci to Switzerland where he was called the leader of the Italian Socialist Northern Republic.
Mussolini was treading on thin ice from the very beginning with Hitler. Italy never had the power to be an effective army ally and Hitler knew this as soon as he realized that North Africa would not be taken and held by Italy. Had a crowd not stomped Mussolini to death in Milan, Hitler would have someone else do it.
Perhaps the worst thing that Mussolini did was cause the destruction of millennium old architectural remnants of its distant ancestors, the Romans, the midwives of western civilization. This, the Romans thought, was the ultimate horror of the worst leader Italy had in the modern age.