….However I'm not convinced Malta falling would be decisive. The key factor is the handling capacity of the Libyan ports and their distance from the front. Even if all the supplies had got through Rommel wouldn't have reached the Nile. Given the naval losses supplying Malta it might have been better for it to fall.
I would agree with you on the necessity of invading Malta, or the ability. By the summer of 1942 Malta had 30,000 troops and a few hundred guns defending it.
While Malta did some serious damage at times (but this was not the usual case) what held up the regular delivery of supplies was not the Royal Navy or the RAF based on Malta but rather the physical limitations on the Italian side. Unfortunately, the standard post-war narrative emphasised Malta's role and this made a convenient alibi for the axis commanders.
Fuel oil for the Italian navy was not just scarce, it bordered on almost non-existent. Germany was already facing serios fuel shortages by September 1941 and found it was not only having to 'short-ship' allotments to the army in Soviet Russia during Barbarossa but also the U-Boat arm and Luftwaffe. In many ways, the high attrition rates amongst the tank and aircraft eased the fuel supply problems but at the cost combat strength.
The second issue was the infrastructure limits found in the port capacity of Tripoli and Benghazi and the ability to move supplies forward without a railway. Tripoli could dock less than five (5) large merchantmen at a time, the rest of the vessels had to wait out at sea, with attendant risks from submarine attack. Benghazi could barely handle 2000 tons per month and unloading was often delayed/decreased by bomber raids from Egypt.
The Italian navy delivered more than 85% of the supplies that embarked from Europe. Tripoli, and often Benghazi, had supplies stacked up in depots but no way to move these supplies to the front. By the spring of 1942 DAK's two panzer divisions, PAA's 90th Light division, Italian armour, motor and leg infantry (a total of just 10 divisions) were using almost as many trucks as a German army group used in Soviet Russia. Furthermore, at any one time as many as 50% of the Italian and German trucks were off the road missing vital spare parts or tires.
And so the supplies the troops so badly needed sat in the ports while Rommel blamed the Italians, Kesselring and Halder for not supporting him (in a side show).