I just want to post a comparison between my piano playing and my organ playing (as of this moment). I still think that my capacity to express articulation on the organ is at a baby stage. I'm a little better on piano.
There's obviously a different articulation approach on the organ. I hear the A-List players and they are so expressive. But an organ has a square envelope, as they say. There is no decay. So I haven't found the answer yet.
Articulation, as you get more advanced is about dynamics at each note, and micro-time control at the note level. These are subtle elements that often cannot be heard by beginners. I can do it to some degree on piano now. Now that I'm able to hear it on piano, it's glaringly absent on organ and it is frustrating.
I'm thinking though that learning control of the organ articulation may add to development in piano control, at least at the time level (clearly not in dynamics).