MCP Servers are not simple wrappers around REST APIs, they can do much more and we will see more advanced use-cases surrounding MCP as MCP clients continually improve their conformance to the spec. Just wrapping REST APIs may be what MCP Servers are now, but that's just because MCP clients still need to catch up in supporting these more advanced features.

MCP Sampling (with tool calling) is one such example, where MCP servers will be able to generate responses using the MCP client's LLM - not requiring an API key themselves - including calling other MCP tools within the "sampling loop", and without corrupting the primary agent's context. This will generate an explosion in advanced MCP servers, although neither Claude Code, Gemini CLI, nor Opencode support this feature (yet).

Once MCP sampling becomes widely supported the pendulum will swing back and we'll see the boundary between MCP tools, async workflows, and generative responses begin to blur.