Every place is a little different based on needs.
At Nike for example, designers (Level 1, Level 2, and Senior) were assigned to functional category teams (basketball, running, and so on for sport focus, and then apparel, footwear, or equipment for product focus). To get to be a senior was near an act of god there. You had to be recommended by your manager, pass an informal yes/no review of all of the directors, and then be approved by the VP of design. The cool thing is that being a senior really meant something there. It meant that you were the best. When I was they were considering adding a principal level, essentially a super senior. Leading each category team was a design director. Usually a team was about 3-5 designers. The design director was responsible for the design language of the category, as well as managing and mentoring the team. Larger teams (5+) also had a design manager and the design director would just focus on design language. For each product focus (footwear, equipment, apparel) there would be a separate design director, then each category then would have a Creative Director that those design directors reported to. IE Running would have a Design Director of Equipment, Footwear, and Apparel, those three report to the Creative Director who oversees the big idea for that category and its execution through all forms of product, packaging, market execution and influences brand campaigns… sounds complicated, but you can see how a structure can be tailored for a specific need.
At frog it was a totally different set up. Each Creative Director had direct reports that they mentored and managed, and also ran project teams according to client and expertise. Project teams would be built for each client based on the need of that given track of work, typically a Creative Director, a Program Manager, and a Resource Manger would craft each project team and may or may not be staffed with some of that Creative Director’s direct reports. In essence, almost everything was flexible, which is what you have to do in a consulting environment where the very shape of the org needs to shift. There I had 4-5 direct reports, but would be running project teams with as many as 15 people and as small as 2.
Where I am now has a very different structure. My role oversees all design decisions, product, packaging, web, mobile and web apps, and marketing materials, but my direct team just handles product and packaging. I have a director of industrial design and several designers as direct reports and then a “dotted line” to the various marketing orgs.
There are many different ways to skin this. The most important thing is to have a structure that is designed to meet your needs and that fosters creativity, flexibility, and accountability.