I am not sure you need to create a new character with all 3 classes for the guardians ability card. I had 2 hunters and a warlock and created a Titan maybe 3 or 4 weeks ago. I noticed I now have the card so I would have got it with the Titan. I have never had a Titan before that though so I am not sure how it works if you have already had all 3 characters. Either way though, if you never created one subclass, it will give you the card once you create the missing one. No need to recreate your existing ones.