I never quite understand why /mcp endpoint is needed.
You can still keep using Rest API with swagger docs and tell the AI to read the swagger docs. It's the same thing. The entire Rest API specification is a lot more flexible than the JSON RPC format /mcp uses.
MCP is fine for exposing tools that don't have APIs, but wrapping an API is an MCP is fine if you like consistency.
Personally, for just tools, I wire up tool calls with context captured via system prompt.