I think one of the things that has made me really sad, watching new divers in the pool and in OW, is how much they struggle. Generally in BCs that don't fit very precisely, they have big problems with stability in the water, as the tank gets a little off center and wants to pull them with it. They kick and fan the water with their hands, to avoid turning turtle.
But soft or split fins don't stabilize a diver very well. They don't take the "bite" out of the water that a stiff, paddle fin does. So a diver who hasn't got the skills to balance the tank on their back (which is LEARNED) also doesn't have a good tool to regain his balance when he has lost it.
I think more experienced divers can use split or soft fins comfortably, if they choose. But the LDS habit of putting all the OW students in splits is not, in my opinion, doing them any favors.
BTW, I have taken some of these struggling divers and put them in my Jets, and had them come out of the next dive smiling and saying, "Oh, that was SO much easier!"