Neither of them could actually lead or follow.
We have a few couples like that here. They dance super-advanced movements with elegant everything, and make no mistakes technically or musically. They're smiling, and seem relaxed and confident. Then you try to dance with one of them . . .
I can't comment on the leader in such a couple dancing with a different follower. I can comment as a leader dancing with the follower in such a couple:
Nothing works.
Even basic stuff is jerky, off the music, and full of tension, because the follower has never truly followed, and is trained only at mini-choreographies with someone who covers any and all errors. With me, they are racing to understand what my body is saying and to figure out how to construct a response. That begets tension, if not actual fear.
The hardest part is sensing their legs. Such followers never have the presence required for communication, nor are they as grounded as is required to be ready to move in any way that makes sense if the leader does something on a whim. They are so used to following a script where they do the same barely communicated movements that they've never gained command of their weight and axis. Both legs "float" in a mixed state somewhere between free and supporting, and either their body feels as if it exists only above the waist or they seem to have two supporting and zero free legs at all times.
With a partner like that, even if I move in an entirely reasonable way on something that's conclusively in the music, I stand a good chance of dragging them off-axis or bowling them over, or just going nowhere. That's because I have no way of reading their body, and they're unready for musical interpretations different from those of their forever partner's. If they were at least present, I could adjust . . . but they have no or too many legs, in effect, so I'm left to guess. If my guess leads me to move in a different time or in another way than they expect, we're doomed.