“... Russian infantry has very poor firing discipline. “Spray and pray” burns a lot of ammo ...”
US infantry may be better disciplined today, but in WWII and Korea we went through a lot of ammo. A GI in a foxhole may look cool and relaxed, but he isn’t. The adrenaline is flowing and if he sees or hears a rustle in a bush ahead there will be half dozen emptying their ammo clip into the bush.
Of course, we weren’t professionals then but citizen-soldiers - draftees.
At least later in the war if not sooner, very well-trained draftees.