@redezem All I can say is that it works for us.

The point of agile isn't to get it done faster, its to get it done right with faster feedback. The military have this concept of the OODA loop, which needs to be as short as possible to let you react to new information. Agile has the same idea.

No, requirements are not meant to change, but the reality is that users cannot envisage the new software and how they will work with it. Waterfall blames the user for that. Agile works with the reality.