Another major issue due also to the huge inertial mass of air is the slower accelerations of the balloon during ascent phases alternating with descent phases, leading to significant loss of power during very long transition phases.
As I find that Magnus balloons are interesting because they can be stacked easily (Omnidea shows two stacked balloons on the video at 1:50 ; see also stacked Sharp rotors) and perhaps could fill the space, I maybe will open a topic on “Magnus balloon ladders”.