What's the difference between "MCP Server Aggregation" and the litellm_proxy endpoint described here?

https://docs.litellm.ai/docs/mcp

The main difference is that while you can get Nexus to list all tools, by default the LLM accesses tools by semantic search — Nexus returns only the relevant tools for the what the LLM is trying to accomplish. Also, Nexus speaks MCP to the LLM, it doesn't translate like litellm_proxy seems to do (I wasn't familiar with it previously).