The ultimate bottleneck was resources, not production. In 1944 the Germans went full tilt with production, using up their stockpiles of resources to create enough equipment to stem the tide, meaning that by 1945 production would not be able to maintain even half the output as the previous year.
The best hope would be to slow the Russians in Ukraine, maintaining the resources in the East, especially Romanian oil, for as long as possible.
The worst that the bombing campaign did was to chew up the logistics of the German rail nets. By doing that, important resources and products synthetic oil could not reach the necessary places. Let's not even mention food.
The very best thing that could have been done about the air war was to have an entirely different Luftwaffe leadership before the Battle of Britain. By having an efficient replacement system, ie rotating aces back to training schools to impart combat experience instead of the "fly 'til you die" Goering method, then the airwar could have stayed favorable for much long. That and not fighting the Battle of Britain.
I am convinced that a Mediterranean option in 1940 after the fall of France would have netted the best results: LW forces in Italy and North Africa, taking Malta while it was not very well defended, coordinating with Mussolini better and preventing him from invading Greece, intervening earlier in Africa.
It wouldn't hurt to actually release some LW assets to the navy to help them spot for U-boots.
As the invading Russia, I do think that was the right decision. Stalin did not trust Hitler and was going to attack him when he was strong enough, which is why it was better to do it when Germany was strongest, not Russia. Obviously the campaign could be better conducted, but that would mean changing the generals, many of whom made the bad decisions before 1943.
A breakout attempt at Stalingrad could not have hurt, the first of many bad decisions made by Hitler.
Kursk, the next major one, if launched in May when it was originally supposed to, could have resulted in a much better outcome, leaving the Soviets unable to respond effectively. OTL, with nearly two more months of perparation, when the majority of the defense positions were built, the Russians were still beat up, but able to launch three counter offensives in short order, wrecking the German armored forces. No doubt that similar attacks could be made at other places on the front, but I doubt their effect would be the same if the Kursk salient was properly chopped off.
Also, by having the attack not occur at the same time as the Sicily Italy invasion, forces can be switched around with more ease than was the case OTL especially if the post-Kursk Russian offensives had already occurred by July.
Thereafter, a mobile defense, not necessarily the backhand blow of Manstein, coupled with a more competent Luftwaffe and the war could very well go on until the Soviets are running major manpower deficits. The longer it takes to capture the Ukraine and other occupied Russian territories, means the less manpower the Soviets will have available and the more conscription in their current territories, thus faster reduction of available manpower. It could end up a vicious cycle where the Soviets potentially have enough men, only they are under German control and offensives are launched simply to liberate more manpower for recruiting.
Of course all this presupposes the Germans to make much better decisions than historical, so nothing is certain.