I think Hitler was pushing for the oil fields as a first priority. And just because the Russians were yelling and crying for a second front, does not mean the rest of the world should hop to it. Seems like Stalin was bullying and putting undue pressure on the USA and the UK to help them out.
We were just not ready. We could have invaded France, but we did not have air superiority, we did not have the trained troops or equipment at this point in the war. It would have put our troops up for a slaughter.
If Stalin had not killed Generals and generally purged the military ranks, maybe he would have had experienced military leaders who could have made their fight less costly.
Besides, we already had our “second front” in the Pacific. I hate that so many Russians were killed, but it helped us, the UK and the rest of the world that Germany attacked Russia instead of the UK and that Hitler used so much of his resources (including about a million men lost) against Russia.
One of the principles of war I was taught (which we got from the Germans IIRC) is concentration. As much as he needed oil, instead of repeatedly dividing his forces Hitler should have gone for the jugular, Moscow and secondarily Leningrad, and only after securing the key objective turn south. Thank goodness he was a lousy general.