This is the problem looking at the"MTO" as a single theatre. The distances involved are huge. Winning the war in Libya / Egypt (North Africa) still leaves a huge task before getting your hands on significant quantities of oil.Winning the MTO would have been a major accomplishment for the Axis. They might have been able to access petroleum in the middle east, and prevent the Allies from using the Suez. And with Malta falling, their fleet & air power could concentrate on blocking Allied forces from breaking into the Med from Gibraltar.
Once you get to the Suez Canal you are still 750-1000+ miles as the crow flies (longer by road) away from the oilfields around Kirkuk in Iraq and at the head of the Persian Gulf with its big oil refinery at Abadan.
There was a small, even by WW2 standards, oil field in Egypt on the Red Sea coast IIRC, but no refining capacity. There were refineries at Haifa in Palestine (British mandate territory) and at Tripoli in Lebanon (Vichy French controlled until mid-1941), but they drew their crude oil supply by pipeline across the desert from the Kirkuk oilfields.
Britain maintained a lot of troops in the ME outwith N.A. during WW2 under various commands at different times. Check out 9th & 10th armies. Immediately prior to war with Japan the region was being reinforced against the possibility of Soviet collapse or Turkey entering the war on the Axis side.
The Med was shut to through shipping traffic from mid-1940 to mid-1943. A lot of the resupply was unloaded at ports like Suez at the southern end of the Canal. In mid-1942 A part of the Med Fleet, including the subs, was withdrawn to Beirut & Haifa. Losing the Canal would not have ended the fight in the ME.
From mid-1940 there was really 2 naval campaigns in the Med. The Med Fleet based on Alexandria (about 150 miles west of the Canal) and Force H based on Gibraltar. Both about 1,000 miles from Malta. Once Malta falls those forces are free for other purposes. Force H also had responsibilities covering the Atlantic, as during the Bismarck chase.