The bottleneck of the Italian/German supply efforts to North Africa wasn't the Med, it was the fact that the Italian holdings in North Africa could only transport a certain nummer of supplies.
I agree. IIRC it was port capacity that was the primary problem; if additional supplies had arrived, they'd have resulted in the ships waiting longer to unload. Also, another problem is getting equipment from teh available ports to the front line. There was a railway from Alexandria to El Alamein, supplies coming the other way have to use trucks and there weren't enough to go around. There was a reason why all the German offensives stopped at roughly the same place.
Remember that allied supplies came around the Cape anyway, they're not subject to interdiction
So, upshoot is fighting in North Africa gets a bit harder, that's all. No great sweeping advances with ubergeneral Rommel (grotesquely over-rated as he is) winning the war single handed. That just isn't on the cards.