I think a big part of why this discussion is coming up again and again is that people assume the way they are using AI is universal, but there's a bunch of different ways to leverage it. If you have an agent which runs within a product it usually cannot touch the outside world at all by design, you do not need an explicit sandbox (i.e. a VM or container) at all because it lives in an isolated environment. As soon as you say "we use CLIs not MCP" well now you need a sandbox and everything else that goes along with it.

If you can tell ahead of time what external connectors you need and you're already sandboxing then by all means go with CLIs, if you can't then MCP is literally the only economical and ergonomic solution as it stands today.