speaking from personal experience, my mare WAS trained this way. I never knew until about a year after I adopted her and came into contact with her former owner by chance. She became so petrified of people that these "trainers" were unable to sell her. She was picked up by a local dealer where this woman bought her BECAUSE SHE FELT BAD FOR HER. She literally had to be ace'd to be backed, loaded, feet trimmed, anything.
Yes, my mare probably would have seen a far worse fate if her former owner didn't buy her up. But let me tell you this horse RUINED her 20 year riding career, she became so afraid of what this mare could do that she still to this day will never mount a horse again
And just to give you a time frame: it took my horse 5 years of sitting untouched in pasture (while her former owner still had her) and then another year and a half (once I got her) of being handled and retrained under saddle for her to trust people again and be ready to even START a discipline. Not weeks, not months, I'm talking YEARS. Even still there are some things that she will never get over...
Treating an animal this way can and WILL scar them for life. Just please be totally sure that you can see this horse all the way through if you decide to go forward with this and be ready to handle whatever you cannot change. The time, money, and patience involved is something that is not for everyone. Not saying that you can't handle it by any means (i somehow did!) or that this horse will be the same way, but just want to give you a picture of what you COULD be up against