Also steam has diff based patching (which requires accress from whoever is running the steam binary) which makes a lot more sense than how package managers operate for large packages, imagine downloading an entire 20 gig game every time there was a minor bugfix, it would be very obnoxious.
Unless the design of both package managers, and how steam games store settings/etc both change radically, this really is the only workable solution.
Luckily, you will still be able to share steam folders cross user, just simply give both users read/write access to the folder.