A lot of people talk about how important this gun was from a design perspective since it became a template for assault rifles, but how impactful it was in the war itself? Were the regiments who used it simply became unstoppable forces or no StG 44 was only important on a design level and paving the way for future guns?
As I have said on several occasions before, had the German government of 1944 set out to operate a boutique weapon design and military doctrine consultancy, it would have done good business in the 1950s. Unfortunately, they were trying to win a war against determined and well-equipped opponents, who were less concerned with finesse in weapon design (the .303 Lee Enfield was literally a 19th century design) and more concerned with actually winning a war.
Discussion of the impact of individual weapons is something of a red herring, as the military position of the Wehrmacht in 1944-5 was catastrophically bad, losing ground both to the east and west every day and struggling for logistics on both fronts. Did the introduction of a new weapon requiring new ammunition and (for best use) new doctrine and training help or hinder this? We'll probably never know
There is not a great deal of documentation of the operational use of the StG44. Soldiers were told not to use the gun in full-auto, and the magazine follower springs were not strong so the guns were practically (and later, actually) limited to only having 25 rounds in the magazine. If the net effect was to provide the Germans with a semi-auto weapon firing an intermediate cartridge then the practical effect relative to both Russian and American forces is probably quite small, as they had ample supplies of semi-auto and auto infantry weapons and, crucially, no shortage of ammunition or replacement guns.