Valid. There are many ways to do it.

But for enterprise there may be teams, each developing their own way to do it. Then there will be many different ways that it is done throughout the enterprise, which is hard re: governance. Better/easier to adhere to an industry standard which can be audited, especially for enterprises where that is a legal requirement.

That isn't a reason you should use it, just an explanation about why someone has to use it.

>reaches out to service.com/agents.md for a fresh copy every so often and uses that to resolve the relevant tool calls.

that is basically what MCP is. except it answers all the questions that your version handwaves away - how often do you get a fresh copy, how do you describe the relevant tool calls, how are the tools organized, and how does auth work.