Notes:

Although it is rarely ever talked about, the British Army, more specifically the RAF, were very important to the Greco-Italian Campaign.

The Greek Army's naval forces were essentially non-existent, and their only submarine got destroyed after it attacked some transport ships traveling to Albania.
The British bombed Italian ports in Otranto and Taranto, causing heavy damage and casualties to the Italian Navy.
Their air operations begun six days before the war with Greece was even declared, and continued further to the end of the war.
The Brits also delivered their own planes and allowed the Greek airforce to use them

Overall, both the Italian and Greek armies suffered about the same number of casualties, 13 thousands each, with a very high number of Italian POWs that gave the Greeks the edge overall.
However, the military personnel delivered for the war against Greece was of over 400 thousands men.

Germany's assistance allowed the war to end much faster, as the Greeks had no chance in handling both armies simultaneously.

Is Italy Europe's Soft Underbelly? Yes.

Did invade it make the war end sooner? No.
In fact, the campaign in Italy had the opposite effect, and created an internal and outer civil-military war that lasted till 1945

The Allies rejected the plan of invasion through Northern Italy and went through the British Channel instead, for what today is known as the D-Day