The main benefit of MCP today over just giving an agent a CLI is of course that you can be a lot more certain about what the agent can or can't do.

Yes, an agent with CLI access and access to making HTTPS calls is a lot more efficient for most tasks, but also a lot more unpredictable and with much higher blast radius if it starts misbehaving compared to one that only have access to exactly the tools and data sources you want it to use.