Ok, here my 2 cents 'on topic'
Fighters
Until the MC 202 Italians had no planes to counter the Zero in any field except ruggedness. The Zero was slightly faster and much better than the 'serie zero' in ALL other parameters.
The 202 closed the gap outprforming the zero in some parameter, but remaining inferior in others (mainly armament, manoeuvrability and range)
The Serie 5 was better than the zero, but in 1942-43 the jap had the Raiden, in late 1943 the Ki84 and the next generation of 44-45 Jap fighters was better than the Serie 5. Could the Serie 5 have been better than them if developed after 1943? Probably yes, but there is no proof.
Bombers
The Piaggio 108 was better than any jap bomber, but was built in amateur quantity. The SM 79 although belonging to a previous generation, was roughly equal to the Jap twins (Betty etc.). But the good and bad points of the planes was opposite.
Recon
some very neat Italian 2 and 3 engined design, but nothing as advanced as the 4 engine Kawanishi. Also the range was completely different: the japs were designed for Pacific, the Italians for Mediterranean sea.
Radio + Electronics
low quality for both
So, if we limit the discussion to historical data (1940 to 1943 and actual production figures), my choice goes with the Japs: the Serie 5 fighter was not produced in enough numbers to turn the tide and the Zero would have made a huge difference until mid 1941 and hold herself until 1943 against the Serie 2 and the few Serie 5, paving the way for the bombers.