You are mostly right except forgetting that not all SaaS companies want their users to shoot themselves in the foot by exposing the entire API surface and all of its quirks and risks to AI agents.

Furthermore, In many cases some APIs, for better or worse, are not even sufficient. For example, the Notion MCP has full text search capabilities. Their API allows searching by title only. I don't know why but I am sure there are reasons.

MCP looks redundant until you start working with real users that don't know a thing about AI agents, programming and security.