This is BS myth-making. If he was a casualty in 1941 I'd bet he never saw an M1 Garand, and the SturmGehwer was not even out yet (StG44 means it came out in 1944!)
As for the AK: the modern AK -- the AK-74 -- is not the loose-tolerance weapon firing the mid-power cartridge. It's more like the tight-tolerance M16, firing a light-calber, high-velocity round. That would necessarily make it more difficult to maintain than the original AK-47.
He didn’t recover quickly from his wounds. He began work on the thing late in the war, and didn’t finish the design until 1947. Of course he saw the M1 and the StG44. Of course he took into account what he could learn from observing those weapons and from accounts of their field performance.
The beauty of the AK47 design is that the damned thing works. It doesn’t have to be kept spotless. It doesn’t take a natural -born mechanic to keep it in working order in the field. And it doesn’t need to be real accurate since most infantry combat either is at point-blank range, or involves firing in the general direction of an imperfectly spotted enemy.
The M-1 was designed in 1924 and was standard US Army issue by 1936. Why wouldn’t he be able to get one? We had open trade routes to Russia in 41. Kalashnikov has consistently denied that his design was based on the German StG44.
The Sturmgewehr design dates from the 30’s, and the first prototypes were field tested in 1942. The gun was issued under the names Mkb 42, MP43, MP44, StG44, and Stg45. The Garand also dates from the 30’s. Read a book.