The M-16 was buggy, not an inherently bad design. If it had another few years to bake before being rushed into combat, it would probably have avoided the bad rap.
Given a few more years to bake, maybe it would have achieved parity with the already fully-baked AR-15? It seems like the perfect example of "Not Invented Here" syndrome and didn't need to exist in the first place.
The last-minute management-induced requirement of new ammo is an unfortunate but normal part of the project management process, and is usually part of that decade or so required to get a reliable system into soldiers' hands.
Yea. There was a massive training problem, no chrome bore at launch, and a few largely unearned bad rep regarding the size of the bullet.