it's mostly true but the mcp also installs the knowledge of that REST API in a standard way so that a user can ask "what's projected revenue this month?" and it'll know how to hit your company brain and answer
Or just write good API docs that humans can use too.
most users i'm dealing with are not doc-reading developers. even getting them to tell claude to use tool X is pretty hit or miss whereas claude already knowing what tool to use is 100% hit with correct mcp tool descriptions.