The instinct is to frame this as a binary — hire an agency or build a team. In practice the better question is not who runs the account but what operating model your marketing needs. The right answer changes as the business changes.
An in-house team offers proximity, product knowledge and control. It also carries fixed cost, key-person risk, and the challenge of staying current across fast-moving platforms with a small team. An agency offers breadth, specialist depth and elasticity, but only earns its place when it is genuinely accountable to outcomes rather than billing hours.
Start with the constraint, not the org chart.
If the requirement is clear and contained, what you need is consistent, well-run execution — an always-on model, not a bigger team. If the constraint has moved between channels, you need active strategic direction connecting the disciplines. If the organisation itself is complex, you need a model designed around governance and multiple stakeholders.
Framed that way, the question stops being agency versus in-house and becomes which operating model fits — often a combination of internal ownership and specialist execution support.