I think the bigger issue is that Waterfall is often not "Waterfall".

Sure there's a 3000 row excel file of requirements but during development the client still sees the product or slides outlining how the product works and you still had QA that had to test stuff as you made it. Then you make changes based on that feedback.

While Agile often feels like it's lost the plot. We're just going to make something and iterate it into a product people like versus figuring out a product people will like and designing towards it.