I will throw in my 2 cents worth. Maybe one could average all our opinions and come up with something useful. Then again maybe not.
I have owned around a dozen of the AK’s, about the same number of AR’s and SKS’s. Maybe 5 or 6 Mini-14’s and not a single mini 30.
First of all, the AR is the gold standard. Nearly all are very accurate and a lot are extremely so. Next comes the SKS which is a pretty good shooter. I hardly ever shot them over 50 yards but they would usually do an inch or so at that distance.
The AK’s seemed to me to do a little better than everyone said but still not great. I would guess maybe 2 inches at 50.
The worst of them all were the Rugers. I wished so much that they would have been more accurate as I really liked them. Unfortunately I never had one that would do better than around 3 inches at 50 yards. They all seemed to do about the same.
I sure hear you on the Mini-14. I wanted that rifle to shoot well, it was just so damn nifty handling. Your grouping sounds like what I got, So poor it was impossible to adjust the scope to bring the “group” into alignment.