Yup. This is often why smaller companies are dominated by poor leaders as well. There may not be many that many other voices and the non assertive people realize they are not being valued and leave or they don't join to begin with.
The later I get in my career the more I realize I care a lot about who my manager will be.
Good leaders, by definition, are the kind of people that will elevate the voices of the non-assertive-but-right people.