Granted the soviets did easily their fair share of the war , making a meat grinder for the Germans. But in a 1v1 situation , dont you think the industrial might of the USA would overwhelm the Germans? I always remember hearing the USA referred to as awakening "an industrial and military beast". It would be interesting.
As for the bulge , great section to read into. Showed the German potential in 1944 was still there , and with ample use of weather and other events could be potent. But as mentioned , the allies were just too numerous in the ground and in the air sadly.
Weather was a major factor in WW 2. It helped the soviets win, because the Wehrmacht was not prepared for such harsh winters.
As to the 1v1 between USA and Germany, if Germany were to face only the USA after conquering the USSR, then with all those resources they could defeat the US. But just the German Reich without the Lebensraum resources of the east would probably not defeat the US. It would be a tight battle.
No one could say for sure. The US were a major power because no one attacked them on their own soil so they had time and peace to develop their war industry.