New production isn't being chewed up on the Eastern Front though, so while the Germans will lag behind superior allied industry the gap will narrow a bit. They also have conquered far more resources and industry to produce with.
Let's see how many aircraft the German will save, then, by not covering the Eastern front, assuming that the aircraft were distributed 50/50 between western and eastern (they weren't, historically, as the shift to covering the west more began in early 1942, but for the purposes of this, let's assume 50/50 for the last 6 months of 1942, the earliest when they theoretically could beat the Soviets). Let's also assume that the German fighter losses were approximately 10% monthly, again, on the low end for this period of the war. (we'll assume the high end, constant 20%, as the upper bounds). Now, set the maximum number of German fighters available as the same as were available in Jan 43, which is 1770.
So, 885 fighters assigned to the Eastern front. Over 6 months, that would mean at 10% losses, the Germans would have lost 531 aircraft. Make that 1062 at 20% losses. As such, the savings are large, but it comes out mostly as a wash with the US. After this point in time, the discrepancy merely widens.
If we plot that out at constant 20% losses through the end of 1944, the Germans would save roughly 5310 aircraft, while the US + UK save 13721 aircraft that would have been Lend-Leased through the same period. It comes out mostly as a wash, at best.
That, and Calbear and others have gone over how the Germans can't utilize their conquered territory to produce equipment nearly as efficiently as possible. Slave labor is not near as efficient as regular labor, captured factories must either be relocated or have to be produced in region, etc. The Germans would get far more use out of captured munitions than out of the industries, at least in the short term. (Combine that with the brain drain that would be associated, as many Soviets would flee after the USSR surrenders, along with them needing to run their own industry).
I don't mean the Spaniards, I mean the Kriegsmarine and to an extent the Regia Marina. They can make great use of Spain.
They lose a neutral port where they could have docked in safety, while gaining ports that either provide the same benefits as the Italian and French ports in the Mediterranean while the Atlantic ports don't offer much more than the French ones. The only benefit of Spain is to block the straights, potentially, which means moving massive amounts of German artillery in range of the rock and hope that it falls (though it can be relieved by the sea rather easily).
By 1942, the German losses were already starting to mount at sea, and Hitler ordered the major surface raiders pulled back to prevent a British invasion of Norway. At most, they spent time raiding convoys in the North Sea, slowly being whittled down to the point where
Remember that the Italian Army is in far better shape from not losing its soul in Libya
Did the Italians simply cede Libya and not bother to fight for it after their losses in late 40/early 41? Because that puts the Allies square in control of North Africa in mid 1942, if not earlier.
Italy lost 40,000 as PoWs at Barida and Tobruk, and afterwards at the Battle of Beda Fomm, the British surrounded the Italians and captured the entirety of the 10th Army. There were a total of 130,000 PoWs taken. This is all
before the PoD, as this is what prompted the Italians to request German assistance in the first place.
So, at this point, the question is do the Italians double down on their own, possibly withdrawing forces elsewhere, or do they withdraw in their entirety? If the former is taken, their losses are even higher than OTL and North Africa grinds on for roughly the same amount of time. If they choose to withdraw, they save roughly half of their losses compared to OTL, but they give up all of North Africa to the Allies, who will soon be moving into French Africa as well, this time from Tunis.