M1 Carbine accuracy

[firstflabn]

I simply mean that as designed, it was meant mainly for rear echelon troops.

That's incorrect. Take a look at the first page of War Baby! Development of the carbine was requested in 1940 by the Chief of Infantry to arm personnel of the infantry regiment. In the 1940 T/O, a bit over one third of GIs in an infantry regiment were armed with pistols.