Ever done suburi? Being able to cut decently is a pre-requisite for doing meaningful sword kata, wouldn't you think?
Same thing with empty hand work. Being able to structure your body decently is a prerequisite for any kind of empty hand technique.
I've never visited Sagawa Sensei's dojo, but every aikido dojo I have visited does a variety of basic footwork and stability exercises. (Though not all of them recognize the aiki-relevance of such exercises.) And there's video of Ueshiba Sensei engaging in that sort of practice, too.
Thanks for asking about suburi!
There is no formalized suburi in Yagyu Shinkage ryu. We have paired kata. In the process of working to get better at our paired kata, we learn to cut decently...in my extremely humble opinion we learn to cut more decently than if we had spent the time doing suburi.
But we've also got some guys who practice another line of Shinkage ryu - the true transmission from Kashima - and they do in fact have formalized suburi. But there aren't many sword schools that do it.
In my opinion, it's not at all a prerequisite to perform abstract exercises *before* learning technique. A good kata is structured to give you these fundamentals *at the same time as* teaching technique, and laying the foundation for the spontaneous generation of technique that meet the needs of a combat situation.
I'm not saying an approach where you abstract fundamental into an exercise is bad, it's just not my thing. And in terms of classical Japanese martial arts, its not the norm, particularly solo exercises.