Oddly, I'd say headcount can often be a driver of complexity.
In two ways, one being that more people legit need a more complicated system. You want that so that they interact with the system, not with each other.
The other being a bit of a Parkinson's Law. That is specifically that you will expand work to fit the allocated time; but I posit that you will also expand work to fit the people doing it. So, more people pushing ideas into the codebase will keep more ideas in the codebase. Even if fewer would work.
In two ways, one being that more people legit need a more complicated system. You want that so that they interact with the system, not with each other.
The other being a bit of a Parkinson's Law. That is specifically that you will expand work to fit the allocated time; but I posit that you will also expand work to fit the people doing it. So, more people pushing ideas into the codebase will keep more ideas in the codebase. Even if fewer would work.