I watched your OP vid the other day. I was not too surprised to see that the M4 worked while dusty. Mine always have. Plus, this seemed to be a relatively new, top of the line carbine (which should be expected to be reliable) not one that may have seen better days, with possibly years of questionable maintenance.
In my experience, malfunctions with the AR/M16 platform are almost always magazine related. But I keep mine squeeky clean and lubed, too. With decent ammo and my magazines I have 100% faith that all of mine will work.
But in the real world good magazines can be hard to come by. Aluminum M16 mags are rated by the military as "single use", but are often reused for years. Eugene Stoner said they were designed to be used for no more than 30 complete loading cycles. They are disposable and wear out quickly, especially when run hard.
This is why the HK mags are so highly sought after in A&I. They are far more durable, being made of steel, than standard aluminum GI mags.
What I don't like about AR's is the "twang", and the fact that a bent/broken buffer tube makes it a lightweight club.
But the platform has always been reliable for me.