I've seen teams be organized a number of different ways, but I think the actual staffing of people and distribution of work is less important than the creative concepting and production process. My general thesis on advertising at scale is that it should be really boring: when companies are doing it well, it's because they have put a number of high-performance processes into place and are executing on those. If your team's output and performance is dependent on "aha!," lightning-bulb-over-the-head epiphany moments, then you aren't being systematic and methodical about growth and it's unlikely that you'll be able to consistently scale advertising spend, profitably. Creative concepting and production is at the very heart of how a marketing team works, so I think that should be the most deliberate and disciplined process.
Before I answer the question more directly, let me define a few terms:
- A creative concept is the general idea that you're trying to get across in the ad; I think of it as the narrative of the story you want to tell with advertising;
- A creative variant is some specific version of a concept that might vary from other versions in very slight, impercetible ways (eg. the CTA button is a different color).
This diagram depicts how I think of a performance marketing team's workflow at a very high level:
I think teams, especially on mobile, tend to focus too intently on #3 (Campaign Management and Optimization) without devoting enough energy and resources to #1 and #2, which puts them into a vicious cycle tailspin of trying to salvage performance by cutting budget. A lot of times, this happens as a result of scaling at a pace that doesn't require a regular injection of new creatives on a short timeline: if you're able to grow from $100k / month to $1MM / month over the course of six months by only adding in a few new videos or static Facebook creatives every month -- because at that scale of spend, if your product resonance is broad enough, your creatives won't saturate very quickly -- then lack of new creatives might simply be a foreign concept by the time you're at $2MM / month and seeing performance degrade. So if you're only focused on #3 as part of the marketing workflow and see #1 as just something that needs to be done every so often, you'll similarly focus on campaign optimization to remedy performance degradation, and without new creative concepts, that usually results in cutting budget.
So with respect to organizing the team: I believe the entire marketing team needs to be involved in the workflow diagrammed above, not just the team members responsible for producing creative. This is important: the media buyers tend to have the best "on-the-ground" view of what types of creatives are working at any given point in time, so they can provide very valuable input into the first stage (concepting and production).
That said, I like to hold a weekly Creative Meeting with the entire team where concepts are pitched and organized by priority. I also like to maintain a slack channel (#Creative or similar) where anyone can drop screenshots of ads they've seen. In the weekly meeting, the team goes over the submissions as well as any freeform ideas that team members pitch and parse out the promising ideas. Those promising ideas go into a Trello board or Airtable table, and then someone (either the Creative Director or Head of Marketing) prioritizes the running idea list and picks a handful of ideas to send to production that week.
Production timelines can vary depending on the creative format (video, playable, static banner, etc.), the input footage required in the creative (eg. a live action video), and who is making the creative (if it's being outsourced or produced by an internal team). Some creatives might take a month to produce; others might take a day.
The key to making the diagram above work efficiently and on a regular cadence is to get to a point where each part of the process (concepting, testing, and campaign management / culling creatives) is done every week. The only way to get to that point is to make sure that the creative production funnel is wide enough to ensure that at least one or two new creatives are being scaled up from test every week. In my answer to How do you test brand new creative themes on Facebook when your current creatives are performing really well?, I talked about my idea of the "half life" of an ad creative. The only way to be excellent at performance advertising at scale is to pre-empt the half life of ad creatives. If you can constantly refresh ad creatives before campaign performance degrades, you'll avoid the reversion to the mean I discuss in that thread and keep performance at an elevated level.
Coming back to the question: the team might be organized into media buyers, a creative team, and analysts, but again, I think everyone should have equivalent input into the creative that is ultimately produced. There shouldn't be Chinese walls between groups: the media buyers need to be able to influence what creative is produced, and the analysts should be able to tell the creative team which concept themes perform the best.
Similarly, the creative team can't have veto power on concepts or broad powers to influence the quality or art direction of the creative that is produced. Strict brand guidelines and "quality" standards are the Achilles heel of a performance marketing team: the team should have the full freedom to test anything. If brand consistency is truly important in ad creatives at scale, then that informs not just the creative production process but everything the marketing team does -- it's a very big decision that doesn't just manifest itself in what creatives are produced. I've seen teams get completely hamstrung by brand guidelines while trying to work in a performance marketing framework like the one diagrammed above. If you're operating under the tight strictures of brand, you're not a true performance marketing team (which isn't a bad or good thing -- it's just a reality), so being organized like one simply gives you the worst of both worlds.
With respect to creative testing, I outlined my approach to that in this answer: What's the best way to test creatives on Facebook?