It sounds like where we're primarily in disagreement is whether the defining difference between Duty Finder and Party Finder comes down to (complete party vs incomplete party) or ("I don't care who I play with" vs "I care who I play with").
The ability to accommodate both complete and incomplete parties is a feature shared by both DF and PF. The ability to be selective about prior clears is not.
Insofar as functions apply to content that would be in the Raid Finder, RF is in this peculiar in-between spot where it has all the functionality of a duty finder, with a single added feature that really falls in the demesne of the party finder.
Code:Do I want to queue with a complete party? | +---- No: Do I care if people have cleared content already? | | | +---- No: Queue Duty Finder | | | +---- Yes: Queue Raid Finder | +---- Yes: Do I have a complete party already? | +---- Yes: Queue Duty Finder | +---- No: Do I care if people have cleared content already? | +---- No: Whether you use DF or PF doesn't matter. | +---- Yes: Match with Party Finder. ---- vs ---- Do I care if people have cleared content already? | +---- No: Queue | +---- Yes: Match with party finder
And I'm ignoring those arguments for good reason. One-off, no commitment parties happen just fine in PF -- see the many Wondrous Tails parties. You can join one of those and get a win without ever saying anything to anyone, and then leave. Current trials and raids would work out just the same.