Yes, it can be, but we also have to watch the growth cycle of the tree during the year. Late fall and early spring are the best times of the year to disturb the roots.

Many of the trees that I had used poor soil on (because I was cheap and used potting soil I could afford/find) were displaying similar poor quality root results. When I see two or three long coiling taproots at the bottom, and the all the other roots are barely spreading out into the rest of the pot because the soil there is wet and spongy, I know the the tree could have benefited from a better bonsai soil.