One of the worst AR's I have even seen was an old-school Maine Bushmaster, early 90's with purple anodizing. That was just cosmetic, but the canted front sight that turned out to be the whole barrel indexed wrong and the locating pin put in about 15 degrees off. Guess what, the bolt was only about 25% locked up and it eventually sheared the lugs off the bolt. Neighbor brought it over for me to look at after "it was really loud last time I shot it" according to him. He had bought it new, probably put less than 1,000 rounds through it.
I did own a ban-era that had the AK-74 compensator on it. It had a full 16" barrel, so I was able to chuck it in a lathe and turn it down to removed the blind pin and put a regular flash hider after the sunset. It shot well, but I got rid of it and got a Colt 6920 in 2011. There was nothing wrong with that Bushmaster, and probably should have kept it and rebarreled it.