What does the typical articulation of an average organist look like?
Soprano is more pronounced, with more space between the notes while others - especially the middle parts sound more or less legato.
More or less? Probably more.
It's not that middle parts need more articulation. They need more attention without which they can all sound easily muddled like a painting standing in a dark room.
If you can't articulate clearly and evenly all the voices, your listeners will have a hard time to appreciate the intricacies of the musical texture you're producing.
If they can't understand the piece, chances of them getting the most of it are slim.
But if you do the homework of showing the ornate palace of polyphony by making sure your articulation in the alto, tenor, and bass is on par with soprano, then some of your listeners might come to you after the performance and tell you how deeply moved they were with your playing.
Big clarity, big impact.