If you build connectors for yourself or your team, you probably can skip MCP because you can tell your friends to install CLI or whatever and provide extra prompts for your CLI.
If you have external users, then you have to use MCP, which comes with how to use each endpoint and etc. MCP is what their current apps e.g. Cowork, Cursor support out-of-the-box.
In that sense, MCP is very much not dead
If you need a network boundary, what MCP provides that REST API + llms.txt can't do?
OIDC? Ease of deployment in a company?
You can have your IT department configure an MCP for the org, and your regular non-technical users click a button and login with their account the service. Then they get all the tool calls authenticated as themselves.
The AI probably can figure out. However, Claude Code and other tools are built to support MCP. This means MCP is probably more reliable than using REST API + llms.txt.
Standardization. Who writes llms.txt? Everyone writes their own? Will agents still behave the same?