Answer
The right method depends on timing, data shape, failure tolerance, and operational ownership. Some flows need synchronous APIs, some work better with batch or event-driven exchange, and some need transformation or queueing so the IBM i side is not forced to behave like every cloud app around it.
Buyers should compare methods against the actual workflow rather than chase a fashionable pattern. The best fit is the one that is understandable, supportable, and reliable for the systems involved.