Waterfall was bad due to the excessively long feedback loops (months-to-years from "planning" to "customer gets to see it/ we receive feedback on it"). It was NOT bad because it forced people to think before writing code! That part we should recover, it's not problematic at all.
If people actually read the original paper by Royce 1970 they would see that it's an iterative process with short feedback-loops.
The bad rep comes from (defense|gov.) contracting, where PRDs where connected to money and CR were expensive, see http://www.bawiki.com/wiki/Waterfall.html for better details.
When you do most of the thinking before you start implementing the whole thing, and if you think that that's enough, then you've missed the unknown unknowns part, which was a big talking point in the mid 2000s, back when the anti-waterfall discourse got going (and for good reason).
But I expect the AI zealots to start (re-)integrating XProgramming (later rebranded as Agile) back into their workflow, somehow.
Thinking before you start implementing the entire project is doomed to fail. Thinking before you implement each features/user story is usually rather important.
A waterfall model with short feedback loops iterating on small tasks is not the worst thing in the world
If your feedback loop is hours or days, I don't think it's bad you spend some time thinking ahead of doing. Oh, you missed the unknown unknowns? You'll hit them soon enough anyway, this is not a model that encourages abstract planning with no action taken, for extended periods of time....
The problem with "AI zealots" is seldom that they spend too much time planning ahead. If anything, it's the opposite.
