I am not sure about the rootbound part.
Most of my cym hybrids bloom the following season after dividing and repotting. Of course, I get better performance in subsequent seasons but that is probably because the plant has grown more pseudobulbs rather than being rootbound.
They do like to stay moist during the summer though. So more roots in the pot probably equates to more water being stored in the velamen instead of flowing out of the pots.