1- you stated eastern front was based on manpower.
This wehrmacht could not win since it had less manpower than SU.
That does not mean that the Wehrmacht cannot win (or whats more relevant: fight the front to a standstill), it only meant that victory through a quick strike was unlikely, the EF shielded the Soviets from the German economic advantage. The environment amplified and favoured their strength (which was not the case in Finland).
AGC could have attempted an attack on the capital in 1941, whether it would have bared success is another question (how deep did 9th Army penetrate at Orel?). What's more important is, that the war was not over in 1941, but in 1945.
Was it impossible for the RKKA to destroy the German Army groups in 1941 or 1943? No, but the chance was slim (in 1943 the chance was actually quite large).
A lot of things changed, but not the performance of the armies (barely, to the negative), rather the number of men the Allies/Soviets mobilized.
Why would the Allies and Soviets cooperate? The Soviet bloodloss enabled the Allies to come back to the continent. Why did the Allies have so many men? Why was the axis unable to extract such enormous manpower out of the 200 million they controlled?
At the end of 1942 the RSFSR was down to new cohorts. Why would Belorussia or Ukraine or the Kazakh SSR, Poland and others support Moscow? They were not fond of their rule. Well, the Nazis imposed a war of annihilation, a race war and Germany was surrounded by nations/populations which were hostile to it, while out of their "Germanic sphere", only Austria joined their ranks in greater numbers. Italy refused to commit forces to the same degree as they did in WW1 against the Central Powers. Nations like Sweden had little interest in such an obnoxious ideology and France was considered an arch enemy (despite the collaborationatist Vichy forces). Japan was on the other side of the world fighting China and the US.
Why did Australia, New Zealand and Canada support Britain? Why do they still support them today? Cultural spheres and the former Empire. The world was convinced the Nazis had to be defeated, yet the Soviets were morally on the same level. What I am trying to say: The political stage had the same importance as the war room. Wasn't the free world convinced that Saddam Hussein was evil? Syria was amongst the forces that intervened and the Assad clan was morally on the same level as Hussein.
How did Flavius Aetius defeat Attila? By forming an enormous Alliance, joining forces with his former enemies. Why? Simply because Attila enraged those tribes, which he had pillaged before.
What happens if you attack Britain? USA, Canada and others join the fight. What happens if you attack the USSR? Then all Slavic nations and manpower from their system can join the ranks. What happens if you attack Germany? There is only Germany and Austria. The Germans were playing checkers, the Soviets were chess players. They should have factored this in.
But the logical conclusion to the 1- is :
OKH and OKW were suicidal.
You can see it that way if you prefer, but was Alexander the IIIrd suicidal when he marched into Persia? Were the Soviets suicidal when they attacked Finland or marched into Afghanistan? They could have won, yet they refused to pay the price. If that is the case then they were all rather insane, starting such wars in the very first place.
In WW1, Germany did not expect to end up in a long war either. During WW2, they speculated on a short war in the East and prepared for a long war with France (we know this, based on military and economic planning). We are observing this conflict through history books, with the power of hindsight.
Saddam Hussein had more men than the UN forces, were they suicidal? What would have happened if his forces turned out to have the combat power of the IDF (very unlikey of course)? Would the US Staff or intelligence be able to predict that? Were American forces suicidal when they attempted their (misguided and poorly prepared) operation in Somalia? The entire city mobilized against UN forces, they did not factor this in (they should have seized the TV station, broadcasting propaganda to lay down arms, that would have been a Soviet thing). Was Japan suicidal when it marched on China (they had more men)? If China had the development level of the Soviets, the Japanese would have been expulsed.
You need to realize: The Nazis did not simply run out of men, they also ran out of territory. Take the ability to give ground: If the Soviets could not retreat 900km inland, they would have lost. Manpower or not. France was pressed against the Ocean at the end of May and the Soviets lost ground at the same pace. In the early phase of Barbarossa, the attrition rate exceeded Soviet replacement levels, but when the mud period started, they were able to build up their front strength. Then again, Typhoon was launched, the offensive was initially, tremendously successful but gradually ran out of steam. All Soviet counterattacks were fruitless, they took immense casualties. In 1942 their offensives failed again, until the Wehrmacht overextended deep into the caucasus. In 1943 the RKKA withstood a summer offensive for the first time, from there on, their casualties did not drop. The Wehrmacht did not need the same amount of men as the RKKA in order to be succesful. For the Soviets to win, their manpower generation must have been above a threshold and German replacements must have been dropped and or been kept below 500,000 men per quarter. Liedtke makes the point in "Enduring the Whirlwind". He concluded that Germany had the manpower to win WW2. I agree with this contention on the basis of a different approach. If the war develops in the way as it did, then their chances diminish with every year. Alternatively, if the attrition rate exceeds their manpower generation for a longer period then the Soviets cannot win either. In 1941 this is the case, in 1942 this is the case, in 1943 this is no longer the case with the exception of the last quarter, then Axis power declines.
Now you add another point :
if they took Moscow in 41
Even if they took it, there was no certainty they could hold it, perhaps they pictured an 1812 scenario. Taking Leningrad for instance, would have ended the war quicker, because resources would have been redistributed to a senseless objective, weakening other sectors. The thing is that jesk seems to believe that it was simply Hitlers order that kept the Wehrmacht back, but its the strength of the RKKA that does it, I think we all agree on that, even if it was the mere threat of annihilation. Hitlers primary goal was always Moscow. The failure of other sectors threatened AGC and forced them to give up their positions. Hitler is just used as a scape goat by various Generals in their post war anecdotes (downplaying their own errors, this is not to say that his decisions were always rationale) and no "hidden reserves" existed in 1944 (those were redistributed to other fronts), if Germany wanted to win this war, or fight the front to a standstill, it should have adjusted its strategy after the failure of Barbarossa.
I conclude that they made strategic errors, but they were all based on the circumstances in which they found themselves in and the information they had at that time. The Nazi leadership kept pushing, because they were aware of the fact, that once the full extent of their crimes was revealed to the world, they would be hanged.
Japanese troops were suicidal (as practicioners of Bushido), when they kept blowing themselves up before surrender.