Here in lies the problem, too many people rely on technology to get things done, and when it fails, which it always does, (Just look at the recent problems caused by a faulty update) your stuck left hanging there.
As to soldiers, on the battlefield if your supplies get cut off (Even if it’s only for a short time) you will have to be careful with ammunition or use more basic forms of combat to survive. (This is why they are taught to fight with basic things as well as guns)

Yamaha and Korg are the only two main players left as they did things the way people wanted, whereas others (Even though they were more advanced in many ways) didn’t and fell by the wayside as they couldn’t make a profit. (Exactly the same happened in the home organ market which the arranger took over from, however just like the home organ market became niche, arrangers are now coming close to the same)

If you’re playing an organ (With pedals) your left hand can remain within 1 octave to get virtually all the chords you need, (Many chord changes just require the movement on one or two fingers) so there is actually less chance of getting the chord wrong.

You are perfectly correct about professional players; however for home players it is just as easy to learn full chords as it is 1 finger, (Which is really a misnomer as you have to use more than one finger to get all the chords you want) in fact in their heyday there were plenty of schools that taught people to paly home organ and arrangers and not one of them used 1 finger chord lessons as they were more difficult then learning full chords. (To be honest 1 finger chords just made marketing easier, rather than making the playing easier)

In the end it comes down to what the user wants and so you just choose which is best for your enjoyment. (There are 3 main computer OS (Mac. Linux and Windows) with each of their users claiming there’s is better than the others, whereas in reality they are just variations of the same thing, and you just choose which does what you want the best, with the same applying to home organs and arrangers)

Bill