I would however, venture to say that while we've always fit the above, fighting style has most likely changed. We don't see people fighting with swords and spears, other than in training. Today we see a different variety of guns and knives. So, IMO, we need to adapt to deal with those things.
This is where I have to disagree. Speaking strictly in terms of self-defense, how do people fight that is different from when various martial arts styles were developed?
There may be some differences based on culture or geography, as I mentioned previously. Americans tend to be built differently than Okinawans, for example, and often throw haymakers at the head. However, people still did that on Okinawa, and blocking blows to the head is taught. There may be defenses taught to attacks that are not often seen in 'real life' in America, for example, but what of it? It's all part and parcel of a system that taken as a whole, has defenses to anything an unarmed person could throw.
As to swords and spears, the system I train in has no specific empty-handed techniques designed to deal with either one that I'm aware of. So I guess that's good.
As to knives, well, they were popular then and they still are. So knife defense techniques are taught. Tuite techniques still work.
Guns? Ah, that's different, yes. However, when a gun is within grabbing range, it is susceptible to the same techniques used to effect a hand-held weapon release of any kind, save one does not want the end of it pointed at oneself. At a distance, I am unaware of any empty-handed techniques, new or old, that would serve to protect one from being shot at twenty paces (for example).
In summary, I accept that there are changes in fighting styles. I do not accept that this represents any need to change the techniques which included those types of attacks originally, and for which they still work just fine.
If anything, I find that I may actually have an advantage, slim though it may be. Our Soke was maybe 130 pounds, dripping wet. He had to make his techniques work against gigantic American Marines who were built differently than Okinawans. Taller, more upper body strength, more tendency to throw punches instead of kicks. As a result, his techniques had to be based on body mechanics rather than brute strength in order to be effective. As a rather extra-large sized American, I can have even more effect by using good body mechanics, and my size and strength may even give me the ability to still be effective without having them perfect.
I do not study a traditional Okinawan art because it is a traditional Okinawan art. I study it because it's bloody fantastic. Then and now. I can't think of any way we modern Americans fight today which leaves a practitioner of our style unprepared.
What precisely is it that has to 'change' in order to adapt to modern ways of self-defense fighting?