Now and then someone says something like "Agile methods won't turn a mediocre programming into a star. That irritates me, because bad non-agile methods can make a very good programmer produce mediocre results. Without taking into account their environment, no one will know how good that "mediocre" programmer can actually be.
A star NASCAR driver probably won't win the race, if his car has a flat tire and his support team can't or won't replace it. It doesn't matter how good the driver is, if the car is bad.
One simple idea - that the "traditional" way of developing an application is by implementing one complete layer at a time (whether bottom-up or top-down) - dooms a project to deliver no working features until late in the development cycle. When feedback finally arrives about the features (wrong requirements and/or wrong implementations), there is often not enough time to fix all the problems, and so the developers look bad. The testers also look bad if they don't have enough time to test, or enough time for fixes to be tested.
Turn that idea around - develop one vertical slice of an application at a time, so each feature can be tested as soon as possible - allows the customers and testers to provide feedback early in the development cycle. That can make a difference in how good the final product can be. Instead of projects running late or shipping with bugs, the project has known good features, can ship when enough features have been done, and the developers look so much better. People might say the project has star programmers.
Many programmers and testers have been trained in that "traditional" style. It's assumed in many books, schools, and corporate cultures. I call it "Unconscious Waterfall" when the style is just assumed. It takes a very remarkable developer to do good work in this environment.
In some shops where they do something they call "Waterfall" and they make it work, it turns out that they verify that many features are working correctly early in the project - there are many places where requirements, tests, and code are examined, verified, validated. Those kinds of waterfall projects are pretty rare, from what I see.