From a previous post, your solution is the only way that I found to change the bullet size, but I started noticing issues with rendering/loading times: Perspective XYChart Bullet Render Shape
I was using that method for awhile (with this symol ●), but noticed a significant slow down in the chart rendering depending on the amount of lines using labels. For example, a chart with all circles was loading in 1 or 2 seconds, but when it had all the lines as labels, it could take 10 or more seconds to render everything. The relationship holds true for using a mixture of circles and labels: more labels = more time.
Since then, I've switch 3 lines to circles, 1 to just a line, and left 2 as rendered labels. But with the big circlular bullets, it can become unreadable.