I was under the impression the soviets had the best arty.
It's already been said. Russia had the most artillery. In terms of crew training, mobilization, integration with infantry, logistics, quality of equipment and munitions, communication technology, ballistics calculation technology, artillery theory - USA was vastly superior to all nations in the above mentioned qualities. And other than Russia, USA also had the greatest quantity. A great deal of german/russian artillery was still hauled around by horses even in 1945, USA's artillery was all pulled by mechanized vehicles. Namely the M4 high speed tractor.
If you wanted to put it in simple terms for how COH2 has been balanced, and how I think america should fit into this with its own niche.
Soviets - Good infantry, good anti-infantry
Germans - Good tanks, good anti-tank
USA - Good artillery, good counter artillery (air call-ins).