As I said above - biomechanics is a useful way to sort it all out. But if you only end up with kuzushi, tsukuri, and kake you will never get anywhere near to aiki.
Just my 2c.
An interesting question arises: why is that? Because all those processes are other-centric
A simple biomechanical analogy, let us say you can, as an overly reductionist proxy for budo people, use either a heavy concrete block with an expansive base, or a plastic domino. Time for a showdown... Now throw the plastic domino at the concrete block? Which gets one knocked off its base first (no cute/clever interpretations please as this model is intentionally overly simplistic)? Throw the concrete block at the domino... who do you expect to "win" that encounter? The only thing the domino accomplishes by trying to throw the concrete block is to, well, throw itself.
The reality is, pretty much all of us are the plastic dominos. There are only a small number of people in this world who can be likened to the concrete block, and either they're Andre the Giant, or they put in an immense amount of solo body-conditioning work
to make their body not unlike that concrete block, so that, when encountering all of us plastic dominos, they cut through us like we are simply not there, because really, to them, we aren't.
We don't really pay attention to the biomechanics of what happens to a fly when we swat at it, other than trying not to get bug goo all over our fingers, because really, it doesn't matter almost how we swat at the fly. One way or another it is moving, by its own initiative or by ours.
And yet, these power differentials are real, not metaphorical - such concrete monsters exist, and they started out like the plastic dominos, just like all the rest of us. There are methods for making your body on the right side of that power differential, but they require you to learn the mental/inner
control knobs of your perceived body.
Finding and using those control knobs is what takes years and years of work, not digging through a physics textbook. I can think about vectors and force diagrams all I want, but if I don't put in the horrifying amount of actual work/gongfu/shugyo to figure out what mental commands I must send to, say, my pelvis to control it properly, it is all completely and utterly useless. I'll just end up one plastic domino trying to figure out how to take down another plastic domino.
The physical reasoning in the end can only make us feel better about the work we need to do, but the work we need to do has already been laid out, with clear and simple instructions, by many generations of highly skilled martial artists before us.