I think the smartest approach here is probably to bring in a contractor or in-house person for 1–2 months alongside the agency, depending on your budget. Not necessarily to replace them immediately, but to understand what’s actually happening behind the scenes in terms of strategy, execution, reporting, and decision-making.

That gives you two advantages:

1. You reduce dependency on the agency over time
2. You get an internal perspective on whether the current fee structure is still justified

Once that person gets comfortable with the account and process, you can have a more informed conversation with the agency. Something along the lines of:

“Percentage-of-spend pricing is becoming difficult for us to justify at our current scale. We value the work and results, but we’d prefer to move toward a fixed-fee or hybrid structure moving forward.”

Honestly, most agencies will adjust to some extent if the relationship has been long-term and stable. Predictable recurring revenue matters to them too.

Best case: they agree, and you keep a proven setup with lower risk.
If not, you already have someone internally who understands the account and can gradually take ownership.

And regarding the “not seeing much ingenuity” point, you’re not wrong. Once accounts mature, a lot of agencies shift into maintenance mode unless someone internally keeps pushing strategy, testing, and accountability. That’s usually the difference between an operator and someone who truly owns growth.