I think this ignores two major constraints - the "waterfall mindset" was about stakeholders (customers) believing they can get a finished product in a fixed tim

I think this ignores two major constraints - the "waterfall mindset" was about stakeholders (customers) believing they can get a finished product in a fixed timeline for a fixed price. What happened then was that after the delivery, the stakeholder was wildly unhappy with the result and demanded re-work, but that would be unplanned and un-budgeted. Many ugly arguments and finger pointing would ensue, which could repeat in several "iterations". The other thing which doesn't align with agile was that the stakeholder usually didn't participate in the development. They weren't reviewing the progress, they were typically waiting for the finished product to be delivered.