Joining Party in Progress Experience
I spent half my playtime today joining the first four dungeons as a tank with the Join Party in Progress option ticked. Most of the time I queued instantly, but more than half the time I was thrown into a dungeon with 2 damage dealers who were either AFK or standing around waiting for a healer to join midway. I did stick around and chat with a couple groups, but not once did a healer join.
The feature is neat, the few times I was able to join a full light party and help them continue on and beat the dungeon were great. However most of the time I'd have to explain how the party in progress feature works (or doesn't) and that they'd likely have an easier time re-queueing. After a while this gets tiring, and makes me feel like a jerk for bailing on the poor saps waiting.
I think the feature should only ready you when a full light party can be formed. I feel this would benefit everyone using the duty finder and encourage more people to help groups that have lost members.