You do not need an exit plan for Built to Sell to be useful. The book is really about whether the agency can create value without the founder in every meeting.
Why it hits independent agencies
Most small studios are not businesses in the transferable sense. They are a person with a reputation, a pipeline in their head, and a delivery process only they can explain. That is also operational risk.
Warrillow’s productised-offer thinking is the commercial version of the same problem: if every project is a unique invention, you cannot hire, price, or step away.
What to use
Use it to define a repeatable offer, a delivery sequence someone else can run, and a sales conversation that does not restart from zero each time. Then put the delivery side into the independent agency operating system.
What to ignore
Ignore any implication that every agency should become a packaged product company. Some work should stay custom. The test is whether custom work is a choice or a dependency. Company of One is the counterweight if scale is not the goal. More on this topic: Growth.