Earlier quoted context omitted.
Agreed 100%. I like your metaphor of lead bullets. There's no silver bullet that will win a war, but you sure aren't going to win without putting the lead bullets in the right places.
To torture the armory metaphor further, there are also land mines that you would want to avoid to keep from getting limbs blown off. In that metaphor, traditional waterfall is a land mine filled with plutonium shrapnel and anthrax spores.
Some times you have a clear and well understood problem, and failures are very expensive. You'd be crazy to work on such kinds of environments with anything but waterfall.