The problem is when you think you have mastered those skills you get hit with a real emergency and that mastery goes out the window. At least for those who are not practicing them regularly. And then you do the best you can and hope for a good outcome. It is never guaranteed no matter how well you do what you learned. And quite likely it will be nothing like the pool practice and OW evaluations of your level of skill.
After which you second guess, perhaps feel guilty (even if the outcome is positive) because you will always wonder if you could have been just a little bit better, faster, more efficient. No matter what anyone says. Every rescue I have been involved in, every near miss, stays in the back of your head every time you go into the water with another person. And every time once you've been through a good rescue course you know that in a split second the life of everyone in the water can suddenly be in the balance. And that in order to reduce that risk, because you cannot eliminate it, you have to be proactive and head off issues before they happen.
Even the best rescue course cannot teach you every skill for every situation. That's why stuff is thrown at students quickly, without warning, and sometimes to the degree of being outrageous. And that is to instill confidence. If you can handle a simulated semi panicked diver who has lost their mask and comes up to you trying to mug you for your reg, a real one who is not panicked is a piece of cake.
It is not military training or hazing. Sometimes I wish we could do that in a rescue class to show you what it's actually like to have your mask ripped off and reg ripped out by a panicking diver in a controlled situation. But we can't. The most we can do is make the sims come fast and frequently. I include some type of rescue skill in every class I teach.
The last wreck class I did I built a spider web in a helicopter and had the student swim thru it slowly to illustrate that entanglements happen so fast and suddenly that you may not even feel them until it's too late. After the lesson and we were gathering up the lines he cut and tied up out of the way he turned his back to me and I immediately wrapped myself and my gear in about 30 feet of lines running every which way. Just to see how he would react. He did admirably as I was "thrashing in semi panic". He got my attention and calmed me down. Then he cautiously moved around me, careful to stay just out of my reach and got me "free". He did what he was supposed to do in a situation that he had not been warned might happen. But I have been in the water with him before and this was dive five of the course.
But now he and I both know that he can react to a situation calmly, not endanger himself, and render assistance when something happens out of the blue. Was he stressed? Hell yeah. But he reacted to that stress by using what he had learned previously and applied it to a situation that I guarantee was not in the rescue class he took. Or anything like it. He said so.
So before anyone discounts a tough, ass kicking, exhausting mentally, physically, and emotionally draining class, think about what it is preparing you to do. Which is tougher? A bunch of simulations or a person whose life is literally in your hands for real?