Well, I can feel concerned by your reflexion
I have mapple (trident, palmatum) both in pots and in the ground. I don't root work those who are in the ground because if I 'd transplanted them every two or tree years, they would grow jjust a little faster (if any
faster) than those in a pot.
I already lifted some of these mapple out of the ground and layered them (with various success
) and I plan to follow with root graft. Those trees have big trunk but their nebari is immature, and will stay so for a while even if layering is successful.
This is just that growing good bonsai takes time and that there is no short cut no side effect.