Somebody has to run the account. The usual options are a person inside the company, an agency, or a freelancer, and the choice is usually framed as a budget question. It is more useful to frame it as a question about where the knowledge lives.
Three arrangements
In-house
Fastest feedback loop, best product knowledge, worst platform knowledge. The person running ads usually has three other jobs. Work happens in bursts, and the account drifts between them.
Agency
Platform expertise and a process, at the cost of distance. The account is one of many, the reporting arrives monthly, and the knowledge about your account lives in someone else's head and someone else's spreadsheet.
Freelancer
Closer than an agency, cheaper than a hire, and a single point of failure. When they go on holiday, the account does too.
What actually breaks
In all three, the same two things break: nobody sees the account daily, and nobody can reconstruct why a change was made three weeks ago.
A feed of every change with the author, the diff and a comment thread solves the second problem regardless of which arrangement you chose. When the agency changes a budget, you see it. When your in-house marketer duplicates a campaign, the agency sees it. Handover stops being a document nobody wrote.
Where an agentic OS fits
It does not replace the person who decides what to sell, to whom, at what price. It removes the part of the job that is clicking: pulling the numbers, preparing the change, writing it down afterwards.
In-house, that turns three hours a week into twenty minutes. At an agency, it turns the monthly report into something the client can read on Tuesday. For a freelancer, it is the difference between eight accounts and fifteen.
A reasonable default
Keep the strategy where the product knowledge is, which is usually in-house. Buy platform expertise when the account gets big enough to deserve it. Put every change, from whoever makes it, into one feed so the knowledge stops leaving with the person.