Is this the API surface you're referring to?
https://developers.figma.com/docs/rest-api/file-endpoints/#g...
https://developers.figma.com/docs/rest-api/file-node-types/
Seems read-only, which means we're stuck with the MCP for updating Figma files... unless you've found a workaround there too?
You can use their plugin API.
https://developers.figma.com/docs/plugins/
This is what I use. Load a little shim plugin and control it with whatever you want. I made the plugin poll an http server that listens for commands.