the M16 was loathed
Not by my dad. He said if you cleaned it like you are supposed to clean every gun you depend on, it was plenty reliable.
The original M16, without a forward assist or chrome-lined barrel was a turd. It was quickly replaced by the M16A1. With a more regimented cleaning procedure, it was fine.
The ammo they used in that era was light (52 grain?), fast and fragile. From a 20" barrel, at intermediate range, the bullet would disintegrate on impact with a human body, with good effect. The stopping power problem crept in after the war, as heavier bullets were used. Those bullets were designed to penetrate body armor and barriers better, and didn't disintegrate on impact. Rather they just punched a hole. It got even worse with the M4's 14" barrel.