Bokeh, to make a stab at the etymology and original use, even though the Japanese word simply means fog or haze, in photography terms it most certainly originated as an allegory of the practice of applying gradated print colour on woodblocks when printing Japanese woodblock prints.
Above is not a wood block print (just something I had handy on my HDD), but it perfectly illustrates the principle and the Japanese sensibility for gradated colour.
Also historically, whether it's SP or AP that is easiest to implement and on whether that has any bearing on the preferred method, I think is quite undecided.
From what I can glean it's very, very close.
Even if we take into account the difference between leaf and focal plane shutter control.
Both can in principle be controlled equally easily with a simple capture the needle system. And of course if there ever was a slight difference, when you bring solenoid, voice coils and motors, in more modern cameras (70's and up) into the equation, it's very much the same.
Outside of a very few special cases, it's neigh on impossible to get an accurate impression or idea of how bokeh and DoF is going fall in the photo, by stopping down. You can get a very rough idea of what is going to be in focus, but it
is rough, because of course the screen get's darker and grainier once you stop down.
Thus you are left with imagination, which no matter the experience, will not be accurate at all with all the variables. Especially where it really matters, with tele lenses that are almost fundamentally slowish in handheld versions and therefore present a darker image in the finder.
Part of my, perhaps implicit, reasoning here is that shutter priority is actually a better way of controlling aperture, than directly controlling aperture.
Most of the cameras that has SP as only program, has some accommodation for letting you know what the aperture is going to be, so it's not completely up to the camera.
This is all about speed of capture. The second you are doing something measured and precise, like a landscape or a still-life you will use a tripod and manual exposure.
SP is just a version of P (program) with a hard skewing in one direction.
Depending on the lens, you have very different possibilities WRT shutter speed. That's part of the genius behind the lens modes on the Canon T70. There is just build, in making it even easier.
Staying in the sweet zone of optimal apertures of the lens, if you are that way inclined, is also fully possible with SP.
The difference between 1.4 and 2.8 can be quite small and as said impossibly hard to judge or imagine accurately. Even harder with higher apertures like the difference between f8 and f11.
On the other hand with shutter speeds you very often have an idea of what is reasonable in a given situation, what you absolutely need or can get away with, with a given lens. And you might also have some idea, that you want a certain amount of motion blur and even camera movement blur, or contrary that it should e avoided as far as possible for that particular photo.
What I often observe with me and others, is that out of habit or laziness, that the aperture will either go to full open as default, or you will set it to optimum aperture and forget about it.
And then it will
stay there, until you are forced to think about it. That will lead to suboptimal and boring photos IMO.
Not so with shutter speeds. There you are forced to think about the implications all the time.
Now, I'm not saying that AP doesn't have its place. It certainly does.
I just have come to the conclusion that it often becomes a glorified substitute for P mode, with none of the inherent variety that is build into that.