Great samples of your work. Thanks for sharing.
I like to do ball point sketches too, mainly for the same reasons as you. However, long ago my pencil work didn't seem to improve so I switched to ball point. Did so for about four months. I soon learnt that ball point doesn't have to be just for sketching but also for fine work too. It is a new way of drawing. The ink builds up around the ball and constantly needs wiping. Finer hand motor skills (light, steady an swift) is needed. I used to buy a few pens and picked the least leaky one for fine work. I got so fine that I could always feel the ball role. After three months of fine work I went back to pencil - wow, what an improvement.