A lot of good arguments can be made about how the U.S. has failed to control the costs of developing and fielding advanced capabilities. Sometimes they just plain make bad design decisions, like with the M1A1 or F-35. But I don't think there's a valid case that advanced capabilities confer insignificant benefits vs. large quantities of less-sophisticated systems. You ideally want a good balance of both and you need the understanding and empowerment on the acquisition side to control costs.
Re the M-16, Jim Fallows wrote a great article decades ago: https://www.theatlantic.com/magazine/archive/1981/06/m-16-a-...