Headless CMS Use-Case for Admin Portals

I'm new to the Headless CMS world, but I've started some dabbling and think it's pretty helpful to get your content backend up and running quickly. I've been struggling with the proper applications for it however, coming from a Microsoft Stack web dev background where for web apps I usually develop a front-end for normal users and an admin back-end for admin users (with custom business logic), and a web API. My question is, does the headless CMS adequately replace the combination of the API (for serving content) and the Admin backend (with its custom business logic)? If it does or can, what's the best approach for implementing the custom business logic? (Is it building on top of the source-code, and/or using web hooks)?