You don't need MCP for prompt templates and context resources. Those are both just forms of prompting.

I'm not sure what you mean? LLMs can only be interacted with using prompting. Even the tool call response from OpenAPI is them just wrapping the prompt on their side of the API with another prompt.

So everything else is just adding behavior around it.

MCP is a way to add behavior around LLM prompting for user convenience.