Even if your agent has internet access, why waste tokens having it re-discover and re-implement its own API client each time? It doesn't make any sense.

For me, I have a service that has multiple vectors of what would be called an API - PowerShell Modules, WMI, RESTFUL Web Services, some are available, some can do some things, some are more direct, some are not allowed with enterprise security etc.

Either way, I don't do what you suggest. I have self-learning rules and have the models build a well-rounded API engine once, then re-use it with query scripts through skills. Its portable and flexible in many environments.

This is my favorite position, the advantage of an MCP tends to lie more in token optimization.