You do not need to use Monodevelop, even on Windows or Mac to write Xamarin apps. Monodevelop is just the most obvious as it's packaged. And agreed, Monodevelop is not very good.
(Actually to be fair, you'll find the Atom family of tools and related plugins to be not terrible for writing C# code. We can only hope that VSC continues to grow and spread and monodevelop fades away into the 'what were we even thinking when we made this?' it deserves to)
For Mac and Windows, you can download Xamarin Studio which is a bundle of MonoDevelop along with Xamarin iOS/Android plugins and branding. Note that a Xamarin license is only required if you develop iOS/Android projects, all other project types are free without restrictions.