Outsourcing a critical platform is rarely a purely technical decision. It shapes who understands your business, who controls your costs and how easily you can change direction.
Ask these before you decide
Which knowledge must stay in-house for us to make good decisions? What will it cost, in money and time, to bring this back if the relationship fails? Do we own the code, the data and the documentation? How will we measure the vendor, and what happens when they miss? Who on our side has the authority and the time to manage this contract?
If you cannot answer who owns the architecture, you have outsourced more than delivery.
Often the right answer is a balance: a small internal team that owns architecture, data and decisions, with vendors delivering clearly defined work.