Those who have a legitimate amateur or professional standing in boxing, wrestling or mixed martial arts do have some grounds for thinking that a lot of the stylized training to be found in the traditional martial arts are largely useless in fighting opponents who have the desire to hurt you as well as the size, strength and experience to back that up.
Having taught for many years I have also met and/or taught many people who had trained elsewhere in karate, tae kwon do and kung before coming to my classes. In general, the majority had little to show in the the ability to deal with unrehearsed and strong intrusions that weren't done in the style to which they were accustomed.
It's also true that martial athletes who compete and have pressure-tested their techniques are scary physical specimens and that most adults are unlikely to be mugged or attacked by someone of that calibre. In the end, how you can defend yourself is based as much on your ability to be just as determined as the person attacking you as well as on having had some training that involved contact while using simple combinations of techniques that you have practised on people who actually resist those techniques so you know they have some chance of working.
So if physical conditioning, simplicity and repetition of techniques under challenging conditions are largely the answer to defending yourself; why bother with traditional martial arts? You could argue that the traditional training builds health; you could argue that the training can be fun [an under-rated factor in our society] and -- perhaps the most important reason in the long-run -- such training can teach self-control.
It used to be a maxim that "you must know yourself to truly know others" and I think that this is applicable to recreational martial artists. If you can't control your physical actions; you are said to be awkward or uncoordinated and gradually learning to move with grace, with power, with fluidity are all parts of a learning path that can take months, even years. However, to reiterate my earlier point, being that way in solo training does not automatically mean that you will be that way in anything like a real fight.
Aside from learning to control your physicality, there is also the issue of emotional self-control in that a lack of such can affect your actions in class with your peers ["You kicked me harder than we agreed on before sparring. It's my turn NOW!" or "Jeez, mate, your technique is shit compared to the "Desiccating Turd Flung From on High" maneuver with which I just dazzled Sifu" or "I don't have to control myself when we train, suck it up, buttercup, I've been here longer than you have!"].
We've all trained with jerks at some point in a martial arts life-time and I'm not talking about the quality of their physical movement. Some "jerks" are still worth training with to learn patience if nothing else; but others are a waste of gym or studio space and a needless risk to the health of those they work with, especially the newer students that they tend to focus their attentions on.
Oh, and It's particularly heinous when the teacher has poor physical or emotional control. I suspect that everyone who has trained in more than one martial arts school has had the experience of having a coach/instructor who didn't seem to care as much about his students learning as he cared about being worshipped, feared and or making money. Not everyone learns self-control even if their training environment supports it; but in a traditional martial art there should be a chain of command and an environment that promotes growth for the personalities of the students and physical self-control is often the beginning of learning the emotional aspects of that useful skill.
You could also equate self-control with the psychological aspects of being [or becoming] a good sportsman and competitive martial athletes often have a much better understanding of that concept than traditional martial artists. Of course, 'wanting to win at all costs" is also often counter-productive but that topic is beyond my expertise since I have never been a competitive person in terms of sports.
In the end, perhaps we might all be wise to heed the words of the Roman Stoic, Seneca, who wrote many hundreds of years ago: "Men do not care how nobly they live but only how long although it is within the reach of every man to live nobly but within no man’s power to live longer than their natural lifespan."
Copyright Michael A. Babin ©2019