Incorrect and not even close.
Greenfield is easy because nothing matters yet.
No legacy data. No backwards compatibility. No users depending on uptime. If the architecture is wrong you just rewrite it, rename a few services, and move on.
Maintaining and expanding a real system means every change has consequences. You’re migrating live data, preserving behavior people rely on, and evolving the architecture while the plane is already in the air.
0→1 lets you be bold because you can break things. 1→10M is harder because you can’t.
(I'm just kidding, your dismissal just needed a dismissal to make things balanced again)