You are sure right there. I have had several Mini-14s and Ranch rifles. They are neat guns and generally satisfactory but accuracy is a real weak point.
I wouldn’t call them awful but they will usually group about 4 to 5 inches at 100 yards. I have never had one which was really accurate.
Google Mini-14 forums. The common consensus is that a heavy muzzle brake to control vibration of the cheap, whippy barrel helps, often halving group size.
Sending the trigger assembly to Doc or a local gunsmith will also help.