Omnisharp is extremely slow. It becomes unusable for larger projects.
Okay, so what kind of solution are you looking for here? VS Code uses a closed-source LSP server for its C# extension. Rider is it's own custom stuff, of course.
So...where does that leave the Zed team? If existing LSPs aren't good enough, that's not a Zed problem: they're building an editor, not LSPs for your favorite language.
but that's the thing - apart from being editor it doesn't offer anything of substance... if I want to have an editor I can use BBEdit or Vim...