Yeah, I think it along the lines where stabilization is being applied to the brush you are using. Plus since Krita actually more like photoshop and gimp. Sometimes it actually pasting a raster image (or a Mask from the looks of it) over and over and mutating that instead of building up from a single circle like what MyPaint does. So it could have a lot more overhead compared to MyPaint.
This is definitely a question for @davidrevoy if he ever wanders upon here. He probably understand Krita better than all of us since he uses it daily for his Pepper and Carrot comic. I’ll ping him on Twitter too.