Myth: Agile does not work for a large distributed 300 Developer 5 year project.
Do you really need something as complicated as this to build what you are trying to build?
Looks like a classic Mythical Man Month problem. You don’t need no Agile to tell you that your project is doomed.
The fact that Agile practitioners question the very existence of so much accidental complexity makes people feel that Agile cannot scale. But the root of the problem is the scale (accidental complexity backed by flawed theory and irrational expectations) not which process you use.
There are way too many examples of how small teams have built wonderful great software under time and within budget which thrill their users and have revolutionized the way we think about the world.
Small is beautiful and powerful!