Its not just your barn AC, sadly.
I had a horse like what you described...not fun.
I leased with option to buy him, working to pay him off for a set price on inspection cause I knew once we worked his issues he was going to be dynamite, unbeatable and worth a fortune...
He was a investment, not a horse I wanted as a forever animal... Honestly, a means to a end and a way for me to get there.
This horse was never taught the basics to build on, no understanding what was expected taught to him but he was scared off the ground, forced to jump so he jumped huge everything.
He would jump a 2' fence like it was a 5' oxer and clear it with tons of room to spare...scary actually to ride.
He could not do a cavaletti, could not..he did not know how, he was terrified of them.
He vibrated at the show grounds and ring side he shook with nerves...forget what mine then were like.
There was no rating him...point and hang on praying he not crash.
My horse was a product of harsh handling and being rushed, scared and shown abuse so he would jump...once he learned it could be different he became a different animal.
I also saw other horses similar who acted out because they did have pain and their bad behavior was a way they tried to escape pain and rough handling of their face, body and hurts endured.
Some horses though are so wound in excitement, they love to jump they vibrate with anticipation and appear absolutely dangerous and they are to the wrong handlers or the inexperienced.
Many of them that resemble what you describe are not fun to ride, but they get the job done and produce the ribbons that some only care about acquiring...
Not a situation I would want to be associated with ever again.
My horse over time and with slow teaching and great care became a wonderful mount but you could never be rough with him or it was like he would mentally snap and go bonkers...quiet , confident rider who asked he would do anything for..
There is usually a reason, always a reason why you are seeing what you see...and knowing you want no part of it is great too.
There is no excuse for seeing what you see. I worked with all levels and training of horses from H/J to jumpers...most of them would stand ringside and snooze but once on their back they were all business and knew the job they had to do...but "aggressive, mean or nasty" that was never tolerated by me or at the barns I worked at..
Horses had no reason to act such a way as that and learned quickly how to behave through firm, fair handling and consistent care.