I think a good using horse is more than just what this article described.
Several of my successful show horses were also using horses. I think a lot of people just fail to present them with that opportunity, for fear of ruining them or them getting hurt. That I understand of course, but on a level it's very good for them.
I remember on ride #4 or so of colts out at my first job, we'd take them out to gather cattle - Then when the cattle were in, I'd lope them, and we'd put them on the flag. Then the broke horses would work the cattle that the 2yr old brought in. By the time they were three, they were seasoned veterans. I pressed cattle into a trailer and pushed my three year old filly's body up against the door while I latched it and tied it shut on horseback, all the while the cattle were jumping, pushing against her, and causing mayhem. She never moved an inch. Later that year she went on to earn a respectable amount of money in the show pen with the lady I sold her to.
By that same respect, the older sister to that mare was a TOTAL flunk. She wasn't pretty like her sister, wasn't trainable like her sister, and what have you. Her saving grace was that she was safe and you could rope on her. She was fun to work a cow on too, but she loathed dry work and she loathed anything she couldn't chase down. I ended up using her for two years on the ranch and then patterning her on the barrels, sold her to california.
Both of those sisters were "using horses". Yet one of them was a show horse and the other was a can cutter. A lot of the job that the horse is given depends on their mind, and their exposure in training. A lot of them just don't have the opportunity to become a using horse, and will remain useless all their lives except in their specific discipline. It just depends on how you make one.