I get your point. However that was not his/hers...
Not exactly, but Welding Rod, Warp and Quentin expanded/clarified.
Knowledge/experience is not directly based on your wallet/credit limit as you so succinctly put it. But think about it. Maybe you are a former GI, a pro with the AR platform, you will want to buy a Colt because that's what you used in the service. Or if you are running a DD or BCM, maybe it is your 2nd or 3rd AR. A lot of people buy "starter" AR's and upgrade.
Then as the others said, if you refuse to drop big money on an AR, you will probably buy cheaper mags, and not practice as much with it because let's face it, ammo is pricey. But you can save money on ammo by buying crappy ammo. It's also expensive and time-consuming to clean it all the time and all that nonsense.
I am not saying that really experienced people have never taken a cheaper AR to a class and done everything they should have done and STILL had issues. I am just saying, chances are if someone is running a DPMS or BM or <insert your least favorite low-mid-tier brand here> at a class, it is most likely (a) their first AR, (b) their only AR, and (c) probably not an expert at the ins and outs of the platform.