Raid Finder was implemented in 3.3 or 3.35.
With 3.4 all Ex Primals after Ravana went from Duty Finder into Raid Finder.
Also The Creator Savage is located in Raid Finder.
There is a difference between going into the Raid tab from Duty Finder and going into the Raid tab from Raid Finder.
You can find Raid Finder in the Main Menu > Duties > Raid Finder