Personally, with no research to back it up, I think that "kendo" as we understand it today, can be said to have been born when three things happened:
1) protective equipment was developed
2) rules, of any kind, were instituted, and, most importantly,
3) people started training in order to use the practice weapons for themselves as opposed to viewing them as tools to use to learn how to use a real weapon in preparation for the possibility of having to fight with a real weapon.
Without these three things, I don't think there is any kendo, at least as we understand it today. Historically, I do not know the exact date when these three factors coalesced into what became modern kendo.
In the same way, training in koryu is not a real swordfight either. There is an element of real danger in kata, depending on a person's level, the attitude of his training partner, etc. So, proplery done, kata can also help to prepare one for a real combative situation. Although I have never been in the army, it sounds as though the purpose is the same as basic training: create as real an environment as possible so that the trainee learns how he will behave in a stressful and dangerous situation. But, it is not a real fight. As you say, only a real fight is a real fight. Who knows what will happen or what one will do when it is all on the line? I certainly don't, and anyone who has never been in that situation and pretends to know what he would do is talking through his hat. I know what I would like to be able to do. I know what I hope to be able to do. But I don't know what I will do.
Now, based on things I have read, mainly by Ellis Amdur about his experience in Araki Ryu, it certainly sounds that, depending on the ryu, koryu training can be incredibly violent and painful. Even in the free-for-all training he describes in his book "Duelling With O-Sensei", however, they were wearing protective equipment and using practice weapons. The training he describes sounds, frankly speaking, very much the same in spirit, if not in degree, as the kendo training I experienced with the riot squad police. We didn't do a lot of wrestling, but the message was the same: if you can't stand the heat, get out of the kitchen.
It seems to me, based on my personal experience, that a lot of budo training is precisely for the purpose of teaching people to take the heat. As such, the person training must be tested to his or her limits of endurance and courage. I hated training with the police most of the time. They were all bigger, stronger, meaner, faster, and better than me, I was afraid of them, I was always tired, it hurt like hell, and I was always painfully aware of my own inadequacies. There was not a single peson on that squad that I could beat if they put their mind to it. And they always made sure that I knew that they knew I was weak. Humiliating and humbling. But I think it toughened me up a bit.
Anyway, I think that if kendo maintains that outlook it will keep its "soul", since I think that the main purpose of kendo is to instill the spirit of equanimity in the face of adversity and the toughness required to never give up (or at least take a hell of a lot of punishment before giving up, since everyone has their limits). Basically, to the degree that you can conquer your fear, you will be able to fight. I think that that is the main (not the only) thing that kendo has to teach.