I have had low grade AR's (Olympia), mid grade (DPMS) and my current rifle is a mix of LMT, BCM, and a DPMS barrel.
I will say they all did fine for 3gun work, and the occasional coyote hunt. The Olympia was the most accurate of the three (it was however a 20" HBAR and all the others are 16's) and with the addition of a BCM bolt group it ran like a top! I certainly wouldnt poo poo on milspec. Everything BCM does is milspec and I have zero complaints with the fifteen or twenty items I have from them.
Its easy to say " Colt's suck! My cousin carried an AR in the sandbox and it malfunctioned" but your really comparing apples to horse apples in that situation (especially compared to new mass market AR's), you have no history with the rifle in question and your cousin likely doesn't have any history on the rifle beyond when it was issued to him.
The quality of an AR is in direct correlation to the sum of its parts. I would look at a builder you trust, feed it good ammo, lubricate it with Slip 2k, and run the damn thing until it stops working!
I saw two guys show up with fresh out of the box RRA's Operators and shoot a 3gun event. By the end of stage two they were both asking me to borrow lube and show them how to use it. Gas guns like to run wet, keep that in mind!