How is this different from an agency?
No account managers. No junior consultant doing the work while I am on the kickoff call.
I can say that specifically because I spent a year inside a 210-person performance marketing agency. I know how the model works: the senior person sells and someone cheaper delivers.
The structural differences are three. The accounts are in your name from day one. There is no lock-in: nothing switches off if you stop paying. And the handover is always available, whichever option you choose after the build.
Agencies and I can both run your ads for a monthly fee. The difference is who owns what, and how easily you can leave.