Let me start by saying I live in the Peoples Republik of Kalifornia and chose a Mini-14 over an AR simple because the gun grabbers are focused on the AR platform. A Mini is considered "featureless" and flies under the radar in the PRK.
Here are a few of my experiences from my Mini-14 Ranch Rifle, 58x series. I normally shoot American Eagle (Federal) M193 and SS109/M855 that I used to purchase at Wally World.
My recommendation would have been to use a break in procedure as follows:
Disassemble, clean and lube the new un-fired rifle.
Take a bore snake with you to the range for your first shoot
Then as posted elsewhere:
1 shot and clean
5 shots and clean
10 shots and clean
20 shots and clean
Then go no more than 30 shots without cleaning for the first 200 rounds or so.
Disassemble. clean and lube when you return home.
You have missed that opportunity but all is not lost. Start by disassembly, cleaning and lube. Go out and give it another try. Use the bore snake every 20 or so rounds and things should settle down.
I had issues with the distance the spent cases were being thrown. The standard gas bushing is relatively large throwing cases 25-30 ft. I changed them out for something smaller. Check out Accuracy Systems Inc. (https://www.accuracysystemsinc.com/
Yes, I've seen some case denting, though not as severe as your examples. Minor denting has not proved to be a problem in reloading. I've also experienced some case mouth deformities but again, not to the extent of your examples. Mine all seem to come out in the resizing operation. I have so much 5.56/.223 brass that it doesn't really matter if I lose a case or two along the way.
I also took issue with the Aperture (peep) sight which I thought was large enough to drive a truck through as well as difficult to adjust. I swapped it out for one from Accuracy Systems Inc.
Finally, consider adding some rubber/plastic bushings so that the recoil does not eventually damage the receiver.
Just an FYI, I had my Mini-14 Ranch out at the ranch a few weeks ago and let my friend who is a devoted AR guy shoot it. He was surprisingly impressed. Also it shot better groups than his AR did on a recent outing.