I think this nicely illustrates the mental conflict between drills and practical application.
Consider one of the key points of a high spinning kick (taekwondo in my case but the commonality with hapkido is obvious): a high spin draws your upper body down and away from your target. Obviously, the movement of your upper body will differ based on flexibility and the situation.
Now consider a threat: a baseball bat swung at your face. In that case, you are naturally inclined to withdraw the upper body and counter-attack with the big muscles in your legs. I find that a variant of the sparring back spinning kick serves as an acceptable compromise between speed and power: the back kick provides the power and the spin allows me to position the strike at an off angle.
Is this a risky maneuver? Of course. It requires finicky timing. However, it accomplishes one of my major goals (i.e., keeping the bat away from my face) and there's an excellent chance that I'm going to hit the bad guy somewhere and quite hard.
Nothing in the real world will ever match your training. By learning a variety of techniques, you have the fundamentals required to adjust and adapt to the situation at hand.
Or, in this case, at foot.
EDIT: I found the link for the 2004 Olympic heavyweight match. In this case (at about 4:40), the Korean victor saw his opponent commit to an attack and was able to counter with a knockout. As always, you have to remember that sparring is not real life. That said, this video serves as a clear lesson that an aggressor is often more vulnerable than he realizes.
It is explicitly stated by my instructor that you are unlikely to ever actually use the advanced spinning kicks in reality (reality here being defined as "in self defense situations," not in a ring or a duel).
I have been thinking about your instructor's comment quite a lot lately. I have to agree that these are not techniques that you are likely to have to use in real life but not because they aren't practical. These are killing techniques. Look at the knockout in that video: a highly trained expert wearing full head protection was knocked unconscious with one blow. It is likely that a normal person would be dead or permanently disabled.
Hopefully, you'll never be in a position where that seems like a desirable outcome.