API / API-triggered campaigns for transactional campaigns

It may depend on your goals and roles. At my current and past gigs, I've (my team) had responsibility and ownership of transactional performance as well as other triggered use cases - ie, when changes were required to transactional templates we made them, and if there was desire to modify or update these with secondary messaging, we also owned that process.

Overall, we found moving to an event trigger based approach in almost all cases was the best solution, it gave us flexibility on leveraging channels, updating and editing content. We mainly worked with engineering to set up the appropriate events and properties to drive the use cases.