For many years, my teacher assiduously studied Saito Sensei's books and taught Aiki-ken and jo. In the late 1970s he took a left turn and started practising and teaching the kesagiri style of cutting from the Kashima-shinryu, which he himself learned from Minoru Sekiya. I believe that this was much more helpful for him in understanding the aikido of his teacher (Gozo Shioda) and of Seigo Yamaguchi: it certainly made is body much softer and improved his kuzushi skills. This way of cutting is not obviously "stopped", as I understand the Iwama shomen and yokomen cuts are, even though I have vivid memories of him making strong and clean shomen cuts that made the wooden tsuba on his heavy Kashima bokken rattle.
My understanding is that cutting, as a kind of metaphor for hand/arm movement in taijutsu, is through the partner, rather than into or onto them. I currently teach both shomenuchi and kesagiri (a diagonal cut through uke's torso from shoulder to hip) with bokken, but the kesagiri movement, which ends with the sword tip at ground level, feels much more relevant to the way my aikido is going. In particular, it emphasises the spiral use of the body I am learning from my internal power teacher. And, as I said earlier, ukemi feels very different in the two cases.
I'm not sure how well that answers your question.
I think the correct use of sword/bokken has nothing to do with stopping tip at plexus level or at ground level. You can cut or hit still preserving both forms. The real difference is what happens in the moment of the contact of the target. If there is a slicing motion, you are cutting, if not, you are hitting.
From strictly martial point of view, waving bokken/sword in large round movements creates too much openings in my position, so I don't feel very safe. In the other hand it is true Iwama start/stop method creates a very rigid body. If you study koryu sword schools, you may learn correct use of sword and flexible body. But I don't believe in direct translation from sword to empty hand aikido techniques. You need to keep them separated, the influence is done by induction not by conscious cerebral work.
Only after, one may use bokken work as an illustration some aikido principles, because bokken became his body extension. That what O sensei did I believe, but it was misunderstood by many people. They took it literally as a method to learn sword skills