They didn't look badly root bound but it certainly didn't hurt to do the transplant now. I'm not sure about MJ but a lot of high energy plants seem to grow out their roots first until they reach a certain size, they the foliage canopy follows the root mass in size. Sometimes you will see, after transplants, the plant seems to stop(or slow) growing for a while before taking off again. That is because all of the focus of the plant is on adjusting and growing the roots to the bigger space. Sort of getting settled in to its new home before taking off growing again.