Here's what it looks like with the Plasma Brise theme as a QScrollBar:

It can be changed to QSlider but then there's a color that shows the "increase":

It can be hidden with a stylesheet, but then it won't follow the theme (except for dark/light).
Here are examples:

The logical conclusion here is a custom widget. In a pinch we could subclass the MediaSlider/DrawnSlider widget, with custom ticks at every 10%, perhaps with extra code to snap the selected value to the nearest 1%.

But for now a scrollbar will do. I tested this and it works a treat.