In the smaller startup I worked in, there was already a formal hierarchy. We had a VP of Engineering, two lead engineers, and what amounted to a QA lead and a data architect. And all engineers worked mostly in their own areas of responsibility and expertise.

The difference was that most of these senior people did quite a bit of grunt work that in a larger organization would have been delegated. The VP did a lot of program manager work and the leads did a lot of design and development, since they only had a couple of subordinates each.

But because the roles and hierarchies were established, it was usually clear whose responsibility it was to make any particular decision. We had on paper a formal organization suitable for a much larger team. We could have telescoped out to three times the number of engineers without adding any more senior people; the leads and VP would just have spent more time on leadership duties and less on direct implementation. I suspect the presence of the formal hierarchy was why the organization felt very mature.

Are things different in other companies of the same size?