Installing themes, not made simple

[Dasher]

I use to have some site running old versions of CMSMS and recently decided to reinstall them to the latest version. I'm basically stuck at adding a decent theme now, as either they don't work or have to be manually inserted. How is this still "made simple"? How come it's not possible to just import a rar/zip and have the CMS do the rest (making it simple). I really can't remember themes being such a pain to implement in the old versions, what has changed?

[Dr.CSS]

The themes are made by other users of CMSMS and we have no way to control how they do this, most should just be a matter of uploading the XML through the theme manager, or import design in the 2.* ver., but I've seen some that require you to copy paste some thing then upload folders also...