while I don't have any great love of the M1 carbine for what it is, I have a deep respect for what it was able to accomplish, and the US was very fortunate that we were able to produce and field the carbine when we did, and the way we did.
One of the many things that astonished the Germans when they began meeting serious numbers of M1 Carbines was not just what it was, but particularly that there were so many different makers, producing them in large numbers.
This was something the Germans simply could not do.
One of the many things generally forgotten today, after generations of the US being a superpower and world leader is that back then, we weren't and weren't thought of as such by other nations.
The tremendous industrial might and production capability we created and mobilized during WWII was virtually unknown, or disbelieved by most of the rest of the world, until we proved it.
Some people knew, even some of the military leaders of nations who became our enemies, but they weren't listened to by those in charge.
Yamamoto spent time in the US before the war, and knew our potential, which is why he advised against war with the US. His warnings were not heeded.
There is a story (can't verify if its true or not) where supposedly Goering dismissed the threat of war with the US saying "all the Americans can make are refrigerators and razor blades"... according to the story, Galland then asked if he could get some of those razor blades....(which didn't earn him any points with his boss, Goering...)
Small arms on their own don't win wars, there is a lot more involved in that, but if you look at what we fielded in WW II, and were to point to any one person who did more than anyone else to create the successful arms we used, I'd vote for JM Browning.
Our main pistol was a Browning design, and our machine guns .30 and .50 were Brownings. And the BAR was Browning. Our rifles weren't but I think mostly because Browning died several years before the Army went looking for something better than the 1903 Springfield bolt action.
As an intellectual exercise, I think its interesting to imagine what Browning might have come up with, had he lived and kept designing for another decade....