The most skilled Allied commander in the war is generally considered by most History books to have been Zhukov. The Russian Troops weren't really too beleagured, and had the best Tanks in the entire war in the form of large quantities of T34 85s alongside IL1 and 2 Josef Stalin Tanks and KVs. This is born out by the fact that American Lend Lease tanks to Russia were considered inferior by Russian Commanders and relegated to patroling the Norweigan front.
However, U.S. Air superiority would have taken a heavy toll on the Red Army.
Though I was under the impression that Patton, while being in Germany, didn't get too close to Berlin. While he wanted it, the Russians were closer and would get there sooner. Ike just said don't worry about trying, the Reds were going to get there first anyway, and were quite annoyed about the 20 000 000 Russian Dead during the war, and wanted some vengeance, such that it wouldn't be too smart for the American army to get in the way...
The Red Army defeated the Bulk of the Wermacht, in terms of actual fighting, hence the 20 000 000 casualty figure. One day of the battle for Stalingrad had greater casulaties than all the allies during the entire war (true).
However, we should not denigrate the American Role to too great an extent. The Drive from Normandy and the Allied bomber offensive did take considerable diversion of German Resources, which could otherwise have been difficult on the Eastern front. Furthermore, Lend Lease Aid to Russia, while not being too good in terms of tanks, was fantastic in terms of high technology (radios) and Truck, for transport and supply, which the Red army was quite low on. This infusion of mobility meant that the Red Army was able to extend its reach into Eastern Europe far more easily.
Without the West, the war would likely still have been won by the Red army, but would have continued for another 3, or 4 years.