Endpoint count tells you very little about what an integration will cost. How the provider models failure tells you most of it.
One with clear error codes, idempotency keys and a sandbox that reproduces edge cases takes a week. One that returns 200 on a rejected payment, with no replay path, takes a month of building the reconciliation the vendor should have shipped.
We read the error docs before the feature docs. That is our first check on a new provider.