I watched a movie the other night called 'the warrior within' that was made back in the 1970's. I still remember in the 80's when it was said that someone was a black belt that they were typically very tough and you would not dare jump at them. Nowadays everything seems different. You've got BJJ and MMA, JKD, etc. and the practitioners of these styles often will claim that traditional arts do not work.
I'm sure that the more traditional styles, Goju, Tang Soo Do, Shorin-Ryu, Isshin-Ryu etc. offer quite a bit but in the grand scheme how would you take a base system like this and functionalize it? How would you make these systems work against nearly any type of attack. I know cross-training is one answer but what if you only had one traditional system, like Shorin-Ryu for instance, how practical could it be made, and how would you make it work??
Full contact Sparring
Sparring is probably the best answer.
I also think you can do some very focused cross-training without totally sacrificing the style. Some sprawling and techniques for regaining your feet can go a long way. I think CroCop is an excellent model. He trains grappling to enhance, not supplant, his striking.
Sparring is part of the answer, the other part I think is if there is some self defense tactic/technique that is taught, it should be attempted against a resiting opponent. For example, if you are taught a defense to a head lock, once you have gone over the technique and undersdtand it, start pairing off and starting the sparring from guy A has guy B in a headlock.
Pad Work.
When I did Aiki Juijitsu, we worked in partner a lot, but where always pulling punches. We all had excelent control. But we needed to learn to penetrate the target as well.
We used to spar but I found it to be very unstructured and most times it would turn into brawling. Its hard to add sparing if no one has a good concept of how it should be taught or what the goals are.
All arts can be made to work.
It comes down to a bunch of factors. Your personal attributes, both physical and mental. Your teacher's knowledge and experience. Truly learning the system completely.
There are simply not that many teachers out there that can teach their arts completely and not that many students that can make it work.
Some arts are somewhat easier to master than others.
There is a book called "taking it to the street" which deals completely with this. It is more concept based and taking what you already know and making it work for you.
Decent book, he doesn't just slam on other arts saying they are all worthless.
BTW it's by Marc MacYoung
All arts were at one point functional until they were overly codified and ritualized. Then someone spun off to derive/devise a new art which would be functional until it to succumbed to time and codification/ritualization, at which point another frustrated person would spin that off...