Yes youre right for hitler fighting and conquering russia was the end goal. But the idea behind it was that it would allow germany to be selfsuficient in resources so a british blockade coldnt be as damaging as it was in the first worldwar. Once you have beaten them though and have full acess to those resources anyways there is little point in actually going through with it so as i said if hitler was more flexible on his foreign policy it wuldnt have been a problem.
The part where no eastern front significantly helps the african campaign is that a lot of trucks could be spared for it so the big issue of ferrying supplies from the ports to the front would have ben significantly reduced and potentially replacements for equippment lost would be broght there at a faster rate. together that could easily have been enough to secure victory in this campaign.
For the first paragraph that is somewhat true, but that is a big leap from our original premis of just no LL, and is a different debate all together, also no LL does not mean they will be able to knock USSR out of the war.
As for the second paragraph, more trucks don't really help if they can't get them, let alone all the extra fuel they need, to Africa.
Edit: the axis did send substantial reinforcements to Africa that never made it to port, due to allied air attacks.