Re: What is the nature of modern fighting
The nature of fighting that spawned arts such as jujutsu is very clearly different from the nature of fighting in the modern era. Regardless of all other social implications, especially regarding castes and classes, it is not common practice for any significant portion of the population to carry weapons openly nor is fighting in almost any form legal. I don't mean to imply it is therefore illogical or uncommon that fighting would occur, but the rules of engaging in a fight have changed, by means of weaponry (or lack thereof) or law. The invention of guns as a means of inter-human violence means all fights have the possibility of an outcome that was not possible in feudal Japan. If adding a completely revolutionary means of winning a fight - especially one that breaks the common bounds of combat distance and speed (in terms of both velocity of strike and quickness of reload/refire) - doesn't change the nature of fighting, I'm not sure what you can expect would.
I do not care to respond how this applies to the effectiveness of aikido or any martial art, but merely to point out that there are time and cultural factors that have changed the way the average fight occurs. To get past the (hopefully) obvious and to somewhat answer what I think you were really getting at, only direct conclusion is that the effectiveness of arts such as classical jujutsu just cannot be compared to the effectiveness of the same or related arts in modern times.
Though my direct experience applies only to North America, nearly all states share at least the factors of time and technological advances that have changed the way fights can be fought. Regardless of their probability, these advances do exist.