When does each option win?
In-house wins when search is your core product, your client volume keeps a team busy, and you want full control of method and intellectual property. It also wins when a client contract or regulation keeps third parties away from client data. A team you trust and keep fully utilized can be the cheapest way to deliver per client.
Freelancers win on small, bounded, specialist tasks: a technical audit, a batch of articles, a one-off migration. They also win when you already have a person you trust, when the work needs editorial or design judgment, or when you want to test a service without a commitment.
A white-label partner wins when client demand outruns your capacity, when the service is new to you (GEO and AEO are the common case), or when you want costs that follow client count instead of payroll. It also wins when you want consistent branded reporting and prefer to sell and manage rather than recruit.