Well here is where I am so far. I have completely removed Arc, and all associated games (wiped the lot) and gone for a fresh install of the launcher (not through Arc) and it is currently updating the files.
Praying that this works!
Ok, Update on the latest, the good news is I can now play the game after doing a full uninstall and reinstall, so I'm guessing Arc had something to do with it. The bad news is that it updates over 8 GB of game files every time i'm starting it up!