If I don't let the plant get rootbound,I have little reason to break up the rootball.have you ever broken up the rootball? growing tips are not "concentrated" on the outside wall. You should have branching everywhere.
I didn't say the roots were exclusive to the perimeter. They just like that space and grow well there. In a small pot you condense the initial growth, everything finds fresh soil when repotting. It doesn't grow back into itself.
Perhaps the plant sees the edge of the pot as an obstacle. In nature we have small rocks and boulders for the roots to cling to and forces them to branch. These obstacles provide space for air and water. In pots, the perimeter is the only obstacle. Problem with them in pots is that they take up valuable real estate. The better alternative is using extra large pots in the beginning and providing the obstacles. Chunks of char, pieces of coconut shell, what have you....I believe this from dissecting all my rootballs. Many will argue with me. It is really all theory on both sides. What I do know, and I think you might agree, is that by copying nature we are eminently more successful then when we try to force or control it. The further away we get the more we have to rely on artificial means and practices. While nature does not repot, it does create boundaries.