Since when is an assault rifle a high-powered rifle?
The whole design concept is to include a medium power cartridge, between a pistol cartridge and battle rifle cartridge.
Roll back to 1898 with the Mauser battle rifle and the later Springfield .30-06. Battle rifle cartridges require a full-scale machine gun to handle the pressure, recoil, and so forth. Think tripod, and two or three-man crew.
On the other hand, you have sub-machine guns, which fire pistol cartridges.
The Nazi's realized it would be handy to have a weapon that fired full-auto, but had more power/punch and range than a pistol-caliber submachine gun. So, they invented the first assault rifle, the Sturmgehwer. They reduced the cartridge size from battle rifle size to reduce the power. Medium power cartridge.
Certainly not high-powered rifles.