When i looked it up, some said that the advantage wasn't that big because the Americans had many less submachine guns and LMGs due to upper command falsely believing the garand could fill those roles, but I really don't know it that's accurate
u/vonadler answers that exact question here: https://www.reddit.com/r/AskHistorians/comments/3ixrvq/did_the_semiautomatic_m1_garand_give_the/
Long story short, the M1 Garand's firepower advantage ended at the individual level and at the squad and platoon level it was a wash thanks to the lack of automatic weapons. At company level and higher, firepower is dependent on heavy weapons like artillery, and the US had the best artillery system in the entire world.
Note that postwar infantry doctrine became an amalgamation of the American and German system. Nations re-equipped so individual riflemen possessed a significant amount of individual firepower, and also invested into GPMG systems like the Germans did.