It only relies on npm to do the actual pulling of packages and if you so choose, let yarn do the hoisting (workspaces) but everything else, I fail to see how it's simply a wrapper...

There's a ton of stuff like versioning, linking, running scripts/commands, etc across the entire project that npm and yarn do not inherently support.

I definitely think lerna has warts but it provides a ton of functionality that you'd have to ducktape together on your own, which it looks like a lot of people are trying to do as evident by this entire thread...