Fabineau is one I am struggling with. It is not even that it is 'rare', but that skirmish just dies in a few seconds which is a bit ridiculous. So if you want to have a chance getting it you pretty much have to stay next to it waiting for it to spawn instead of actually playing the game.
I think it is fine for the ones that are guaranteed loot in Duels to be very rare outside of duels though. It makes duels a little bit more rewarding. Drop rates could still be increased a little bit though, I agree.