Sorry but that's just [censored]
If some arts demonstration is all acrobatics and showmanship do you really think they train for the opposite? That's just a ridiculous notion that only someone feeling offended would say.
I'm not actually a fan of the acrobatics and showmanship, myself. At the same time real self defense can not possibly be demonstrated because you can't possibly re-create an authentic self-defense scenario on a stage. One can not realistically and authentically re-create a visceral, true-to-life self defense scenario in the dojang. One might be able to come close, but never authentically replicate a real life experience. We train in artificial circumstances. All of us.
The purpose of the demo is not to replicate real life (neither the real life of modern day street self-defense nor the real life of the military conditions under which the art in question was developed).
To assume the demonstrations convey the full depth, scope and magnitude of the art is to assume a movie trailer gives you the entire plot of a movie.