Since the Italians did not participate in the war its impossible to prove any "defects", so we really have to assume they would have performed as well as any other military did 1939-1943. The main variable would be the political/strategic goals of the Italian government. By 1940 it was clear that mobilization for war had severe & unavoidable economic costs. So even if Italy had entered the war its government would have had every incentive to limits it stratigic goals in order to keep economic costs from going wild.
As we saw with Spain joining in and getting battered to crap. Whatever the strength of the Italian forces, they were smart to stick it out - and smarter yet to act as a moneylender afterwards. Suddenly Europe decides it's okay to invade Ethiopia after all (which means Italy joining & losing would butterfly away Haile Selassie's influence on African nationalism - also the rastas)
Leaving aside the how, I wonder how a swift and crushing defeat for France would affect the reputation and influence of Philippe Pétain?
The only thing that would damage him is he was the one surrendering. Nobody'd be keeping paintings of him in their houses after that!
And even if the Germans were about to a hundred Sack of Strasbourgs, I think Petain would still shoot himself rather than do that.