Honestly, the more I train the simpler self defense gets. My current take is that people who develop the work ethic of high school wrestlers, boxers, Olympic lifting, or any other kind of explosive energy training are probably better suited to win fights then the majority of bjj players, aikido players, or karate masters.
I see guys come into the gym with a few years of competitive judo or wrestling and they are just amazing. The same with soldiers straight out of the service. Sure they don't have the hand to hand skills and if you weather the storm you will win with superior technique. But fights in a self defense context don't require skill or technique and rarely have either. It's pure heart in my opinion. Most of us simply do not have it.
Watching this season of TUF made me think about that. One of the fighters loses at least 4 of his teeth. A few days later he is asked if he will take another fight. He tells them "Sure, it's just teeth.". I had a tooth pulled once. I was hold up for 2 days in bed in horrible pain. A punch in my face would of dropped me in a pool of tears. This guy has heart I can never have. I'd bet on him in a life or death situation then most black belts I know or even myself. I can never be that guy.
So the question becomes, can you train heart?
Would not you say that one purpose of training is to give you heart. For me that is all the point of aliveness and resistance training.
If I ask you to jump a 2.00 m wall on a horse and you never ridden before, you will be scared and rightly so, after a few years of training it will be just a jump. as you said the more you train the simpler it gets.
There is no denying that 1v1 professional fighter are great athlete, just as it is obvious that whatever the competitive combat sport you are doing, it is the sum of the best particle for the activity and the rule set.
And that athleticism and the competition put you in good stead in SD.
However it is important to realise and understand the implication of that there is a different set of rule between SD and competitive fighting.
To be honest in Europe and in northern America, you average "civilian" SD customer is not, in all likeliness, going to be very skilled. So it is quite easy to build a an advantage in the skill set and competitive fighting definitely puts you there.
That being said training in jousting is not going to make me good in cattle roping, like 1v1 and SD there is a vast amount of transferable skills however what makes you a good jouster or cattle handler is not so much the skill set, it is your ability to recognise a situation and rea-act to it and you can only get that from training specifically for jousting and training specifically in cattle roping.
As kev mentioned, body conditioning should really be an important part of SD.