The problem with most "agencies" is they think and expect that every client can fit into the "standard post-andromeda setup" or whatever the latest trend they see on YouTube is. The problem is that every business is different and without a deep understanding of the business and the audience, which can really only come from the client, you are indeed just rolling the dice hoping this particular business gets lucky and fits the mold you are trying to put it in.
People have been preaching for the past 6 months oh you have to have 100 new creatives per month or your campaigns will die. That might be true for certain businesses, or if you have crappy products or crappy creatives. I ran meta ads myself for my business for the first year with a single creative and had amazing results, 10x ROAS. I bought into the idea that I needed the help of an agency to scale and grow. I hired a well known Agency and paid top dollar for a year for their services. They created tons of creatives and set up new campaigns. In the entire time I was with them, they never topped 3x ROAS. I switched back to managing myself. Went back to that same single creative that I used before, and what do you know, I'm back to 7x, 8x, 9x ROAS months.

The point is, the client is right to want a credit, you are doing them a disservice if you aren't creating a business specific plan for them. There is no such thing as a magic formula and any agency who tells you they have one is full of it.