How would "a million different tool calls at the same time" work? For instance, MCP is HTTP based, even at low latency in incredibly parallel environments that would take forever.
There's a difference between discovery (asking an MCP server what capabilities it has) and use (actually using a tool on the MCP server).
I think the comment you're replying to is talking about discovery rather than use; that is, offering a million tools to the model, not calling a million tools simultaneously.
It wouldn't. There is a difference between theory and practicality. Just because we could, doesnt mean we should, especially when costs per token are considered. Capability and scale are often at odds.