As far as we speak self defense, none of sports are good for actual self defense.
As i always say - self defense starts when you exit your appartment. The fact that your friend DID LET himself get into situations that require force more than once in his life, menas that either he lives in very criminal area, or that he just lets himself get into those situations. Most problems can be solved by backing down, but people who do fight sports are trained to embrace their ego and test their skills 1v1.
So when a smaller guy comes at me and says : “i dont care that you are big, i can fuck you up” a fighter in me would say : “nope… you cant…”. But a self defense principle would ask for my answer to be more like : “sure you can, bro, i am just fat, i dont fight, im sure you are much better fighter than me, and i dont want to test it”.
A nice example of this is that in 6 years of teaching self defense classes, none of my students ever came to a class on monday with a black eye because of fighting on the weekend. In MMA classes i attended for years, it was a normal scene that some(more than one) guys would come with black eyes or missing teeth after their “fun” on the weekend.
The technical aspect of sports you mentioned also lacks self defense elements, as if you are a grappler, you should never go on the ground because if the attack is real(not measuring dicks) then there are always more than 1 dude, and there might be some waiting around the corner or in the car. You go on the ground, and someone else punches you in the face. I also saw a cool vid a few years back from a street camera, where a bodybuilder got in a fight with some skinny BJJ dude, and the small dude got him into an armbar very fast. The bodybuilder got a knife out of his pocket and stabbed the dude 5 times in the stomach with his free arm.
Grappling doesnt teach you how to get up fast if taken down. It sometimes teaches you the ooposite. Muay Thai is good, but in all my years of experience, i always have been able to teep any thai fighter in the balls. Because they defend roundhouses at leg level, and they hook teeps at midsection but a teep to the balls is in a range they have never trained.
In this case, almost every time a winner will be someone who has trained to anything. Even some Kung Fu bullshit would be better than nothing. A karate nerd vs a meth-head will have a big chance of winning anyways. Trained vs Untrained is always pretty clear cut IF the fight is dick measuring and actually 1v1. Anyways, 1v1 is NOT a self defense, its 2 idiots who allowed themselves to start that.
Not to offend, but your wrestler friend knows he can win and he lets himself get into problems because he feels safe and capable of winning. If the other guy has friends or a scredriver in his pocket, its over and the outcome is very ugly.
Trained at anything, will most likely win someone un-trained.
But BJJ against a dude who has a knife in his pocket is waaay worse than Muay Thai, for example where you can at least try a teep and run.
It is true that lots of street fights end up on the ground, thats why Krav Maga has lots of ground techniques, but a propper Krav Maga curiculum will never do chokes or submissions, but only switch possitions and get up fast the right way(footing and techniques how to get up safe in different distances from the attacker).
The problem with Krav Maga is that it has been made a money making machine and attracts 40yr old IT guys and housewives, so average Krav Maga practitioner is a complete shit, while average “sports” guy is much better as he is forced to be, due to every day sparrings in training.
After 3 years of Krav Maga or any fight sport, the sports guy wins 1v1 100% of time.
But again, 1v1 is not self defense, so when we risk that 1v1 becomes a grappler vs a dude who has a knife in his pocket, the grappler will go all in while my 40yr old IT dude will be scared shitless because he will be able to name 10 possible risks that can happen during that fight and he will just NOT do it.
I always say that for most people my classes or good for just SEEING how deep in shit they can get, so they are just smarter.
Idk how it is in USA, but inb my country most females still see the rapist as someone from Hill Have Eyes crawling out of a bushes in a park at night. They are surprised to know that statistically, 90% of rapes start in a situation where this woman has gone willingly(a Tinder date, a car ride, a hot guy inviting her over) and that the actual rapist most likely is someone she would actually seem as a viable partner(she just doesnt know he cant take NO for an answer).
So when we do grappling i speak about this alot, and in the end - its not that the girl will be better in grappling but that now she knows, where the shit can start and she will be more careful.
BJJ is very good against anyone else who knows it. Its also good 1v1 if you are ok on rolling on the ground where could be rocks and glass and syringes full of STDs.
Muay Thai is much better IF you know how to use it, as you can at least hit and run, or lowkick someone so they stay down and fuck off. That is why Krav Maga has all these elements, the only problem is that it takes much longer time to master because of amounts of topics we look at. Punching and kicking and defenses agains that are only 2 of at least 6 different topics, so actually practicing good strikes we do only 1/6th of the training month.
If id had to chose just one - kickboxing or muay thai, yes… But for self defense i believe you need to know as much as you can, because real problems you can get out of by backing down your ego, are always vs multiple attackers, armed ones, etc. None of the sports are good for this. In fact, in my experience - they are worse. Its much harder to train a good MMA fighter for self defense as it is to train an IT dork. The MMA dude “knows everything” and goes all in every time, and then just gets punched in the back of the head.
As i mentioned - its important to understand that 1v1 fights we see behind the bar are NOT self defense, those are dick measuring contests. A real self defense is a dude asking you for money, you telling him to fuck off and not knowing 2 other dudes wait you around the next corner. In that scenario, of course, it is bad for everyone but a Muay Thai dude cant even answer a tactical question on how to position himself and has never done even light 1v2 or 1v3 sparring.