In my experience, even my first gen home made ARs have been reliable enough to trust with my life. I have shoot thousands of rounds without much issue in the way of FTF, FTE etc and I am the one that likes to run a gun without lube, see how dirty it needs to be, so I can see exactly how it will run in adverse conditions.
The platform is amazing in a lot of ways. It would not have stood the test of time if it was terrible.
Certainly the design has advanced considerably. But just look at how many things stay the same. The difference between an M16A1 and M4A1 is almost trivial. They are practically the same gun, with the M4A1 having an adjustable stock and a shorter barrel. Yes I realize it's more than that, but it's nothing crazy like the difference between an AKM and AN94.
Makes you wonder how different the reputation for reliability would be if the gun wasn't more or less sabotaged in the first place. So many issues in getting this gun into vietnam soldier's hands. No cleaning kits. They were told the gun was self cleaning. Using a powder for the ammunition that was not used in testing.
If the M1 garand was allowed to work with the BAR mags like it was originally intended for, I doubt the M14 ever comes to existence. Interesting timeline to say the least.