what honestly is the difference between an mcp and a skill + instructions + curl.

Really it seems to me the difference is that an mcp could be more token-efficient, but it isn't, because you dump every mcp's instructions all the time into your context.

Of course then again skills frequently doesn't get triggered.

just seems like coding agent bugs/choices and protocol design?

Author here! Biggest difference is composition. MCP tools don't chain (there's people trying to fix that, but it's still true right now).