That's literally what they are. It's a dead simple self describing JSONRPC API that you can understand if you spend 5 seconds looking at it. I don't get why people get so worked up over it as if it's some big over-engineered spec.

I can run an MPC on my local machine and connect it to an LLM FE in a browser.

I can use the GitHub MCP without installing anything on my machine at all.

I can run agents as root in a VM and give them access to things via an MCP running outside of the VM without giving them access to secrets.

It's an objectively better solution than just giving it CLIs.