MCP's are great for adoption of your service outside of developer circles. Non Technical users can click a link, trigger an OAuth flow and authenticate. You can't do that with API. API still is better for developers using a AI via a CLI but MCP is easier adoption for web or desktop based clients.
We hooked up fly.io's sprites mcp to our company claude and now all employees can spin up dev envs and actually prototype, verify or reproduce something before coming to engineering; doing it directly from web or wherever and it's properly authed and sandboxed through their accounts