At the end of the day, the sinker is a POWER pitch. Because of its name, people assume it's only a pitch thrown at the knees. That's not the way it is used in real life at all. The sinker is thrown just like a fastball, all over the strike zone. Up, down, in, out. When Arrieta won the Cy Young award, 48% of his sinkers were waist high or higher.
People talk like the sinker is a change up that needs to be thrown low in the zone to be effective. That isn't the case at all. I'm not saying you should be able to live up in the zone with it if you repeat it over and over, but you shouldn't live anywhere with ANY pitch over and over.