Definitely seems that there's a problem with the installation. We'll go through a complete re-install and see if that helps, there's some files that the Steam auto-removal won't pick up. (Which may have caused your other re-install attempts to not work)
First, we'll manually delete the game's installation folder. Exit Steam if you're currently logged in, and make sure that Universe Sandbox isn't running.
Your installation should be located here, according to your log files.
Users/Promethium/Library/Application Support/Steam/steamapps/common/Universe Sandbox 2/
Just delete the entire folder, and all of its contents.
Next, we need to clear out the player preferences, they're located in the
~/Library/Preferences folder, in a file named unity.[company name].[product name].plist
It should be something like unity.GiantArmy.UniverseSandbox.plist (or close to that) Just delete that entire folder.
From there, restart your computer, load up Steam, and double click on Universe Sandbox 2 in your Steam Library. It should begin to download it again.