I went through this stage with a smaller company and there's definitely this point where you no longer know everyone and things change. Creo however did manage to scale this well beyond 150 people. You don't necessarily need a lot of hierarchy but you do need to figure out a structure. Creo always had a hierarchy, it wasn't like Valve or something. It's just how things worked within that hierarchy.
I experienced this as two phases of growth in the path from ~100 people to ~15000 people: the first phase where you don’t know everyone and the second one where you don’t even know every department/major project.
