I've worked waterfall (defense) and while I hated it at the time I'd rather go back to it. Today we move much faster but often build the wrong thing or rewrite and refactor things multiple times. In waterfall we move glacially but what we would build sticks. Also, with so much up front planning the code practically writes itself. I'm not convinced there's any real velocity gains in agile when factoring in all the fiddling, rewrites, and refactoring.

> Most of what's planned falls down within the first few hours of implementation.

Not my experience at all. We know what computers are capable of.