Ok, so unsubbed from all workshop content then uninstalled game and formatted SSD where rf2 was the only content on the drive. Re-installed rf2, 20 odd gig later, first time booting game, 70 odd installs, including formula E gen 2 again.(which of course failed) Deleted the contents of the 3x formula E gen 2 vehicle folders, removed the contents from Steam\steamapps\workshop\content\365960\1558324776 folder. Seems like vehicle contents for formula E gen 2 is now no longer wanting to install everytime the game starts. Great!! Still not sure why steam thinks I own/want this content, but anyhow working for now.